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 $35.77   5.233%   $37.6418   $37.64   $37.65   $37.60  
  Purchase #2 $47.71   9.519%   $52.2515   $52.25   $52.25   $52.30  
  Purchase #3 $101.42   3.476%   $104.9454   $104.95   $104.95   $104.90  
  Purchase #4 $213.62   13.190%   $241.7965   $241.80   $241.80   $241.80  
  Purchase #5 $200.30   12.863%   $226.0646   $226.06   $226.05   $226.10  
  Purchase #6 $33.62   12.841%   $37.9371   $37.94   $37.95   $37.90  
  Purchase #7 $125.98   7.223%   $135.0795   $135.08   $135.10   $135.10  
  7 purchase totals = $758.42       $835.7164   $835.72   $835.75   $835.70