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 $223.48   10.807%   $247.6315   $247.63   $247.65   $247.60  
  Purchase #2 $239.40   8.720%   $260.2757   $260.28   $260.30   $260.30  
  Purchase #3 $131.89   5.131%   $138.6573   $138.66   $138.65   $138.70  
  Purchase #4 $22.85   13.517%   $25.9386   $25.94   $25.95   $25.90  
  Purchase #5 $109.62   11.232%   $121.9325   $121.93   $121.95   $121.90  
  Purchase #6 $149.30   8.429%   $161.8845   $161.88   $161.90   $161.90  
  Purchase #7 $46.60   5.299%   $49.0693   $49.07   $49.05   $49.10  
  7 purchase totals = $923.14       $1,005.3894   $1,005.39   $1,005.45   $1,005.40