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 $66.96   11.435%   $74.6169   $74.62   $74.60   $74.60  
  Purchase #2 $250.77   12.691%   $282.5952   $282.60   $282.60   $282.60  
  Purchase #3 $161.87   9.658%   $177.5034   $177.50   $177.50   $177.50  
  Purchase #4 $80.35   9.556%   $88.0282   $88.03   $88.05   $88.00  
  Purchase #5 $49.89   5.229%   $52.4987   $52.50   $52.50   $52.50  
  Purchase #6 $226.62   5.151%   $238.2932   $238.29   $238.30   $238.30  
  Purchase #7 $19.65   11.307%   $21.8718   $21.87   $21.85   $21.90  
  7 purchase totals = $856.11       $935.4074   $935.41   $935.40   $935.40