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 $95.39   10.667%   $105.5653   $105.57   $105.55   $105.60  
  Purchase #2 $215.83   7.661%   $232.3647   $232.36   $232.35   $232.40  
  Purchase #3 $192.25   5.419%   $202.668   $202.67   $202.65   $202.70  
  Purchase #4 $81.61   11.634%   $91.1045   $91.10   $91.10   $91.10  
  Purchase #5 $224.36   8.674%   $243.821   $243.82   $243.80   $243.80  
  Purchase #6 $109.98   12.252%   $123.4547   $123.45   $123.45   $123.50  
  Purchase #7 $42.54   4.299%   $44.3688   $44.37   $44.35   $44.40  
  7 purchase totals = $961.96       $1,043.3470   $1,043.34   $1,043.25   $1,043.50