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 $231.63   12.495%   $260.5722   $260.57   $260.55   $260.60  
  Purchase #2 $54.54   8.183%   $59.003   $59.00   $59.00   $59.00  
  Purchase #3 $62.69   10.308%   $69.1521   $69.15   $69.15   $69.20  
  Purchase #4 $156.80   10.128%   $172.6807   $172.68   $172.70   $172.70  
  Purchase #5 $174.33   11.787%   $194.8783   $194.88   $194.90   $194.90  
  Purchase #6 $74.32   13.740%   $84.5316   $84.53   $84.55   $84.50  
  Purchase #7 $110.93   13.284%   $125.6659   $125.67   $125.65   $125.70  
  7 purchase totals = $865.24       $966.4838   $966.48   $966.50   $966.60