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 $167.48   9.228%   $182.9351   $182.94   $182.95   $182.90  
  Purchase #2 $92.35   13.637%   $104.9438   $104.94   $104.95   $104.90  
  Purchase #3 $187.44   6.169%   $199.0032   $199.00   $199.00   $199.00  
  Purchase #4 $180.26   6.468%   $191.9192   $191.92   $191.90   $191.90  
  Purchase #5 $212.26   7.660%   $228.5191   $228.52   $228.50   $228.50  
  Purchase #6 $204.65   10.155%   $225.4322   $225.43   $225.45   $225.40  
  Purchase #7 $213.79   4.247%   $222.8697   $222.87   $222.85   $222.90  
  7 purchase totals = $1,258.23       $1,355.6223   $1,355.62   $1,355.60   $1,355.50