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 $57.54   11.121%   $63.939   $63.94   $63.95   $63.90  
  Purchase #2 $87.59   11.327%   $97.5113   $97.51   $97.50   $97.50  
  Purchase #3 $165.68   5.268%   $174.408   $174.41   $174.40   $174.40  
  Purchase #4 $171.29   6.832%   $182.9925   $182.99   $183.00   $183.00  
  Purchase #5 $88.69   11.744%   $99.1058   $99.11   $99.10   $99.10  
  Purchase #6 $91.46   8.740%   $99.4536   $99.45   $99.45   $99.50  
  Purchase #7 $23.45   12.251%   $26.3229   $26.32   $26.30   $26.30  
  7 purchase totals = $685.70       $743.7331   $743.73   $743.70   $743.70