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 $181.97   11.274%   $202.4853   $202.49   $202.50   $202.50  
  Purchase #2 $164.79   13.441%   $186.9394   $186.94   $186.95   $186.90  
  Purchase #3 $88.35   11.617%   $98.6136   $98.61   $98.60   $98.60  
  Purchase #4 $40.57   12.562%   $45.6664   $45.67   $45.65   $45.70  
  Purchase #5 $197.73   13.445%   $224.3148   $224.31   $224.30   $224.30  
  Purchase #6 $75.70   10.541%   $83.6795   $83.68   $83.70   $83.70  
  Purchase #7 $117.48   13.478%   $133.314   $133.31   $133.30   $133.30  
  7 purchase totals = $866.59       $975.0130   $975.01   $975.00   $975.00