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 $72.58   4.729%   $76.0123   $76.01   $76.00   $76.00  
  Purchase #2 $202.78   9.660%   $222.3685   $222.37   $222.35   $222.40  
  Purchase #3 $130.65   11.631%   $145.8459   $145.85   $145.85   $145.80  
  Purchase #4 $126.28   5.280%   $132.9476   $132.95   $132.95   $132.90  
  Purchase #5 $169.76   13.851%   $193.2735   $193.27   $193.25   $193.30  
  Purchase #6 $136.67   9.197%   $149.2395   $149.24   $149.25   $149.20  
  Purchase #7 $10.90   11.850%   $12.1917   $12.19   $12.20   $12.20  
  7 purchase totals = $849.62       $931.8790   $931.88   $931.85   $931.80