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 $93.59   5.314%   $98.5634   $98.56   $98.55   $98.60  
  Purchase #2 $87.30   3.437%   $90.3005   $90.30   $90.30   $90.30  
  Purchase #3 $43.76   8.359%   $47.4179   $47.42   $47.40   $47.40  
  Purchase #4 $89.52   3.635%   $92.7741   $92.77   $92.75   $92.80  
  Purchase #5 $195.57   6.178%   $207.6523   $207.65   $207.65   $207.70  
  Purchase #6 $8.88   3.244%   $9.1681   $9.17   $9.15   $9.20  
  Purchase #7 $205.34   8.483%   $222.759   $222.76   $222.75   $222.80  
  7 purchase totals = $723.96       $768.6353   $768.63   $768.55   $768.80