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 $62.88   10.241%   $69.3195   $69.32   $69.30   $69.30  
  Purchase #2 $165.69   9.495%   $181.4223   $181.42   $181.40   $181.40  
  Purchase #3 $82.82   5.527%   $87.3975   $87.40   $87.40   $87.40  
  Purchase #4 $212.81   5.860%   $225.2807   $225.28   $225.30   $225.30  
  Purchase #5 $191.93   7.306%   $205.9524   $205.95   $205.95   $206.00  
  Purchase #6 $89.75   5.590%   $94.767   $94.77   $94.75   $94.80  
  Purchase #7 $107.57   4.245%   $112.1363   $112.14   $112.15   $112.10  
  7 purchase totals = $913.45       $976.2757   $976.28   $976.25   $976.30