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 $50.45   7.645%   $54.3069   $54.31   $54.30   $54.30  
  Purchase #2 $23.42   13.485%   $26.5782   $26.58   $26.60   $26.60  
  Purchase #3 $167.44   7.779%   $180.4652   $180.47   $180.45   $180.50  
  Purchase #4 $23.96   5.615%   $25.3054   $25.31   $25.30   $25.30  
  Purchase #5 $144.72   6.427%   $154.0212   $154.02   $154.00   $154.00  
  Purchase #6 $158.81   13.314%   $179.954   $179.95   $179.95   $180.00  
  Purchase #7 $15.82   8.432%   $17.1539   $17.15   $17.15   $17.20  
  7 purchase totals = $584.62       $637.7848   $637.79   $637.75   $637.90