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 $226.25   9.433%   $247.5922   $247.59   $247.60   $247.60  
  Purchase #2 $84.77   3.556%   $87.7844   $87.78   $87.80   $87.80  
  Purchase #3 $216.38   13.381%   $245.3338   $245.33   $245.35   $245.30  
  Purchase #4 $34.52   6.341%   $36.7089   $36.71   $36.70   $36.70  
  Purchase #5 $204.95   10.253%   $225.9635   $225.96   $225.95   $226.00  
  Purchase #6 $77.94   7.770%   $83.9959   $84.00   $84.00   $84.00  
  Purchase #7 $23.25   11.463%   $25.9151   $25.92   $25.90   $25.90  
  7 purchase totals = $868.06       $953.2938   $953.29   $953.30   $953.30