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 $239.77   9.512%   $262.5769   $262.58   $262.60   $262.60  
  Purchase #2 $141.86   6.585%   $151.2015   $151.20   $151.20   $151.20  
  Purchase #3 $154.30   13.352%   $174.9021   $174.90   $174.90   $174.90  
  Purchase #4 $69.85   3.728%   $72.454   $72.45   $72.45   $72.50  
  Purchase #5 $58.86   13.325%   $66.7031   $66.70   $66.70   $66.70  
  Purchase #6 $116.72   7.299%   $125.2394   $125.24   $125.25   $125.20  
  Purchase #7 $6.43   4.578%   $6.7244   $6.72   $6.70   $6.70  
  7 purchase totals = $787.79       $859.8014   $859.79   $859.80   $859.80