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 $216.93   9.846%   $238.2889   $238.29   $238.30   $238.30  
  Purchase #2 $78.47   8.227%   $84.9257   $84.93   $84.95   $84.90  
  Purchase #3 $140.65   6.495%   $149.7852   $149.79   $149.80   $149.80  
  Purchase #4 $177.83   6.852%   $190.0149   $190.01   $190.00   $190.00  
  Purchase #5 $137.78   13.738%   $156.7082   $156.71   $156.70   $156.70  
  Purchase #6 $208.92   8.643%   $226.977   $226.98   $227.00   $227.00  
  Purchase #7 $229.79   9.558%   $251.7533   $251.75   $251.75   $251.80  
  7 purchase totals = $1,190.37       $1,298.4532   $1,298.46   $1,298.50   $1,298.50