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 $55.29   13.361%   $62.6773   $62.68   $62.70   $62.70  
  Purchase #2 $135.65   11.136%   $150.756   $150.76   $150.75   $150.80  
  Purchase #3 $177.77   9.387%   $194.4573   $194.46   $194.45   $194.50  
  Purchase #4 $145.50   8.461%   $157.8108   $157.81   $157.80   $157.80  
  Purchase #5 $178.33   11.639%   $199.0858   $199.09   $199.10   $199.10  
  Purchase #6 $169.71   12.818%   $191.4634   $191.46   $191.45   $191.50  
  Purchase #7 $92.73   12.643%   $104.4539   $104.45   $104.45   $104.50  
  7 purchase totals = $954.98       $1,060.7045   $1,060.71   $1,060.70   $1,060.90