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 $49.64   13.132%   $56.1587   $56.16   $56.15   $56.20  
  Purchase #2 $112.80   12.279%   $126.6507   $126.65   $126.65   $126.70  
  Purchase #3 $211.43   6.832%   $225.8749   $225.87   $225.85   $225.90  
  Purchase #4 $218.36   12.244%   $245.096   $245.10   $245.10   $245.10  
  Purchase #5 $8.30   5.756%   $8.7777   $8.78   $8.80   $8.80  
  Purchase #6 $244.90   9.104%   $267.1957   $267.20   $267.20   $267.20  
  Purchase #7 $142.50   8.233%   $154.232   $154.23   $154.25   $154.20  
  7 purchase totals = $987.93       $1,083.9857   $1,083.99   $1,084.00   $1,084.10