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 $32.83   9.723%   $36.0221   $36.02   $36.00   $36.00  
  Purchase #2 $190.57   4.756%   $199.6335   $199.63   $199.65   $199.60  
  Purchase #3 $229.46   13.159%   $259.6546   $259.65   $259.65   $259.70  
  Purchase #4 $163.25   3.647%   $169.2037   $169.20   $169.20   $169.20  
  Purchase #5 $137.62   11.853%   $153.9321   $153.93   $153.95   $153.90  
  Purchase #6 $98.41   6.501%   $104.8076   $104.81   $104.80   $104.80  
  Purchase #7 $92.99   4.402%   $97.0834   $97.08   $97.10   $97.10  
  7 purchase totals = $945.13       $1,020.3370   $1,020.32   $1,020.35   $1,020.30