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 $77.46   12.807%   $87.3803   $87.38   $87.40   $87.40  
  Purchase #2 $238.54   6.678%   $254.4697   $254.47   $254.45   $254.50  
  Purchase #3 $199.56   13.645%   $226.79   $226.79   $226.80   $226.80  
  Purchase #4 $29.62   13.844%   $33.7206   $33.72   $33.70   $33.70  
  Purchase #5 $162.45   3.666%   $168.4054   $168.41   $168.40   $168.40  
  Purchase #6 $118.38   6.392%   $125.9468   $125.95   $125.95   $125.90  
  Purchase #7 $56.76   10.393%   $62.6591   $62.66   $62.65   $62.70  
  7 purchase totals = $882.77       $959.3719   $959.38   $959.35   $959.40