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 $31.87   11.711%   $35.6023   $35.60   $35.60   $35.60  
  Purchase #2 $203.81   6.228%   $216.5033   $216.50   $216.50   $216.50  
  Purchase #3 $208.56   7.645%   $224.5044   $224.50   $224.50   $224.50  
  Purchase #4 $170.38   8.191%   $184.3358   $184.34   $184.35   $184.30  
  Purchase #5 $200.87   4.194%   $209.2945   $209.29   $209.30   $209.30  
  Purchase #6 $14.79   3.726%   $15.3411   $15.34   $15.35   $15.30  
  Purchase #7 $12.61   3.847%   $13.0951   $13.10   $13.10   $13.10  
  7 purchase totals = $842.89       $898.6765   $898.67   $898.70   $898.60