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 $54.97   5.461%   $57.9719   $57.97   $57.95   $58.00  
  Purchase #2 $149.81   3.546%   $155.1223   $155.12   $155.10   $155.10  
  Purchase #3 $114.69   10.410%   $126.6292   $126.63   $126.65   $126.60  
  Purchase #4 $9.94   10.322%   $10.966   $10.97   $10.95   $11.00  
  Purchase #5 $175.51   4.873%   $184.0626   $184.06   $184.05   $184.10  
  Purchase #6 $115.56   5.663%   $122.1042   $122.10   $122.10   $122.10  
  Purchase #7 $195.66   8.376%   $212.0485   $212.05   $212.05   $212.00  
  7 purchase totals = $816.14       $868.9047   $868.90   $868.85   $868.90