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 $208.39   10.806%   $230.9086   $230.91   $230.90   $230.90  
  Purchase #2 $153.40   10.539%   $169.5668   $169.57   $169.55   $169.60  
  Purchase #3 $210.37   9.238%   $229.804   $229.80   $229.80   $229.80  
  Purchase #4 $74.29   6.135%   $78.8477   $78.85   $78.85   $78.80  
  Purchase #5 $105.48   10.634%   $116.6967   $116.70   $116.70   $116.70  
  Purchase #6 $97.40   4.692%   $101.97   $101.97   $101.95   $102.00  
  Purchase #7 $194.92   5.660%   $205.9525   $205.95   $205.95   $206.00  
  7 purchase totals = $1,044.25       $1,133.7463   $1,133.75   $1,133.70   $1,133.80