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 $63.96   13.157%   $72.3752   $72.38   $72.40   $72.40  
  Purchase #2 $202.97   11.717%   $226.752   $226.75   $226.75   $226.80  
  Purchase #3 $223.91   7.739%   $241.2384   $241.24   $241.25   $241.20  
  Purchase #4 $10.99   5.779%   $11.6251   $11.63   $11.65   $11.60  
  Purchase #5 $88.59   9.869%   $97.3329   $97.33   $97.35   $97.30  
  Purchase #6 $127.88   6.482%   $136.1692   $136.17   $136.15   $136.20  
  Purchase #7 $38.95   11.570%   $43.4565   $43.46   $43.45   $43.50  
  7 purchase totals = $757.25       $828.9493   $828.96   $829.00   $829.00