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 $57.56   6.590%   $61.3532   $61.35   $61.35   $61.40  
  Purchase #2 $49.86   9.392%   $54.5429   $54.54   $54.55   $54.50  
  Purchase #3 $200.89   4.216%   $209.3595   $209.36   $209.35   $209.40  
  Purchase #4 $130.36   4.172%   $135.7986   $135.80   $135.80   $135.80  
  Purchase #5 $86.62   10.549%   $95.7575   $95.76   $95.75   $95.80  
  Purchase #6 $97.36   10.754%   $107.8301   $107.83   $107.85   $107.80  
  Purchase #7 $91.91   5.276%   $96.7592   $96.76   $96.75   $96.80  
  7 purchase totals = $714.56       $761.4010   $761.40   $761.40   $761.50