Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $116.75   10.781%   $129.3368   $129.34   $129.35   $129.30  
  Purchase #2 $245.76   6.756%   $262.3635   $262.36   $262.35   $262.40  
  Purchase #3 $142.68   11.719%   $159.4007   $159.40   $159.40   $159.40  
  Purchase #4 $169.50   7.815%   $182.7464   $182.75   $182.75   $182.70  
  Purchase #5 $107.99   5.173%   $113.5763   $113.58   $113.60   $113.60  
  Purchase #6 $160.73   13.171%   $181.8997   $181.90   $181.90   $181.90  
  Purchase #7 $197.72   3.592%   $204.8221   $204.82   $204.80   $204.80  
  7 purchase totals = $1,141.13       $1,234.1455   $1,234.15   $1,234.15   $1,234.10