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 $14.52   11.811%   $16.235   $16.24   $16.25   $16.20  
  Purchase #2 $172.34   6.344%   $183.2732   $183.27   $183.25   $183.30  
  Purchase #3 $188.67   4.695%   $197.5281   $197.53   $197.55   $197.50  
  Purchase #4 $34.43   6.147%   $36.5464   $36.55   $36.55   $36.50  
  Purchase #5 $90.70   6.340%   $96.4504   $96.45   $96.45   $96.50  
  Purchase #6 $201.94   5.867%   $213.7878   $213.79   $213.80   $213.80  
  Purchase #7 $89.92   3.123%   $92.7282   $92.73   $92.75   $92.70  
  7 purchase totals = $792.52       $836.5491   $836.56   $836.60   $836.50