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 $234.87   6.554%   $250.2634   $250.26   $250.25   $250.30  
  Purchase #2 $210.60   11.427%   $234.6653   $234.67   $234.65   $234.70  
  Purchase #3 $216.68   5.839%   $229.3319   $229.33   $229.35   $229.30  
  Purchase #4 $120.29   5.179%   $126.5198   $126.52   $126.50   $126.50  
  Purchase #5 $78.66   12.546%   $88.5287   $88.53   $88.55   $88.50  
  Purchase #6 $245.66   10.327%   $271.0293   $271.03   $271.05   $271.00  
  Purchase #7 $200.51   9.153%   $218.8627   $218.86   $218.85   $218.90  
  7 purchase totals = $1,307.27       $1,419.2011   $1,419.20   $1,419.20   $1,419.20