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 $94.44   4.372%   $98.5689   $98.57   $98.55   $98.60  
  Purchase #2 $102.71   5.470%   $108.3282   $108.33   $108.35   $108.30  
  Purchase #3 $142.90   6.579%   $152.3014   $152.30   $152.30   $152.30  
  Purchase #4 $15.44   6.731%   $16.4793   $16.48   $16.50   $16.50  
  Purchase #5 $154.63   9.321%   $169.0431   $169.04   $169.05   $169.00  
  Purchase #6 $190.39   5.232%   $200.3512   $200.35   $200.35   $200.40  
  Purchase #7 $91.50   8.225%   $99.0259   $99.03   $99.05   $99.00  
  7 purchase totals = $792.01       $844.0980   $844.10   $844.15   $844.10