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 $237.90   10.135%   $262.0112   $262.01   $262.00   $262.00  
  Purchase #2 $126.96   5.558%   $134.0164   $134.02   $134.00   $134.00  
  Purchase #3 $112.25   6.183%   $119.1904   $119.19   $119.20   $119.20  
  Purchase #4 $66.42   9.699%   $72.8621   $72.86   $72.85   $72.90  
  Purchase #5 $31.93   4.688%   $33.4269   $33.43   $33.45   $33.40  
  Purchase #6 $101.74   6.781%   $108.639   $108.64   $108.65   $108.60  
  Purchase #7 $134.72   4.192%   $140.3675   $140.37   $140.35   $140.40  
  7 purchase totals = $811.92       $870.5135   $870.52   $870.50   $870.50