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 $194.71   6.492%   $207.3506   $207.35   $207.35   $207.40  
  Purchase #2 $156.52   9.807%   $171.8699   $171.87   $171.85   $171.90  
  Purchase #3 $227.79   8.148%   $246.3503   $246.35   $246.35   $246.40  
  Purchase #4 $71.84   4.497%   $75.0706   $75.07   $75.05   $75.10  
  Purchase #5 $56.36   12.120%   $63.1908   $63.19   $63.20   $63.20  
  Purchase #6 $129.34   5.639%   $136.6335   $136.63   $136.65   $136.60  
  Purchase #7 $92.44   9.487%   $101.2098   $101.21   $101.20   $101.20  
  7 purchase totals = $929.00       $1,001.6755   $1,001.67   $1,001.65   $1,001.80