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 $194.85   5.751%   $206.0558   $206.06   $206.05   $206.10  
  Purchase #2 $92.83   5.223%   $97.6785   $97.68   $97.70   $97.70  
  Purchase #3 $182.40   10.840%   $202.1722   $202.17   $202.15   $202.20  
  Purchase #4 $21.90   11.142%   $24.3401   $24.34   $24.35   $24.30  
  Purchase #5 $145.68   3.696%   $151.0643   $151.06   $151.05   $151.10  
  Purchase #6 $58.42   6.201%   $62.0426   $62.04   $62.05   $62.00  
  Purchase #7 $68.97   4.367%   $71.9819   $71.98   $72.00   $72.00  
  7 purchase totals = $765.05       $815.3354   $815.33   $815.35   $815.40