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 $32.93   8.273%   $35.6543   $35.65   $35.65   $35.70  
  Purchase #2 $206.36   8.722%   $224.3587   $224.36   $224.35   $224.40  
  Purchase #3 $46.28   6.476%   $49.2771   $49.28   $49.30   $49.30  
  Purchase #4 $84.30   4.765%   $88.3169   $88.32   $88.30   $88.30  
  Purchase #5 $92.33   8.176%   $99.8789   $99.88   $99.90   $99.90  
  Purchase #6 $161.79   8.806%   $176.0372   $176.04   $176.05   $176.00  
  Purchase #7 $79.36   12.368%   $89.1752   $89.18   $89.20   $89.20  
  7 purchase totals = $703.35       $762.6983   $762.71   $762.75   $762.80