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 $143.74   5.714%   $151.9533   $151.95   $151.95   $152.00  
  Purchase #2 $122.98   5.752%   $130.0538   $130.05   $130.05   $130.10  
  Purchase #3 $208.84   4.265%   $217.747   $217.75   $217.75   $217.70  
  Purchase #4 $159.87   8.645%   $173.6908   $173.69   $173.70   $173.70  
  Purchase #5 $22.69   7.524%   $24.3972   $24.40   $24.40   $24.40  
  Purchase #6 $224.51   5.863%   $237.673   $237.67   $237.65   $237.70  
  Purchase #7 $74.88   11.540%   $83.5212   $83.52   $83.50   $83.50  
  7 purchase totals = $957.51       $1,019.0363   $1,019.03   $1,019.00   $1,019.10