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 $215.85   13.594%   $245.1926   $245.19   $245.20   $245.20  
  Purchase #2 $157.42   12.145%   $176.5387   $176.54   $176.55   $176.50  
  Purchase #3 $96.28   11.479%   $107.332   $107.33   $107.35   $107.30  
  Purchase #4 $13.32   12.548%   $14.9914   $14.99   $15.00   $15.00  
  Purchase #5 $53.45   9.825%   $58.7015   $58.70   $58.70   $58.70  
  Purchase #6 $212.33   7.770%   $228.828   $228.83   $228.85   $228.80  
  Purchase #7 $145.66   13.192%   $164.8755   $164.88   $164.90   $164.90  
  7 purchase totals = $894.31       $996.4597   $996.46   $996.55   $996.40