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 $24.50   8.339%   $26.5431   $26.54   $26.55   $26.50  
  Purchase #2 $156.31   6.202%   $166.0043   $166.00   $166.00   $166.00  
  Purchase #3 $94.26   6.635%   $100.5142   $100.51   $100.50   $100.50  
  Purchase #4 $245.38   9.234%   $268.0384   $268.04   $268.05   $268.00  
  Purchase #5 $132.58   13.559%   $150.5565   $150.56   $150.55   $150.60  
  Purchase #6 $73.96   4.565%   $77.3363   $77.34   $77.35   $77.30  
  Purchase #7 $142.68   11.183%   $158.6359   $158.64   $158.65   $158.60  
  7 purchase totals = $869.67       $947.6287   $947.63   $947.65   $947.50