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 $34.44   4.473%   $35.9805   $35.98   $36.00   $36.00  
  Purchase #2 $54.34   9.154%   $59.3143   $59.31   $59.30   $59.30  
  Purchase #3 $213.36   3.601%   $221.0431   $221.04   $221.05   $221.00  
  Purchase #4 $194.47   11.426%   $216.6901   $216.69   $216.70   $216.70  
  Purchase #5 $5.47   9.369%   $5.9825   $5.98   $6.00   $6.00  
  Purchase #6 $233.70   12.708%   $263.3986   $263.40   $263.40   $263.40  
  Purchase #7 $126.58   4.760%   $132.6052   $132.61   $132.60   $132.60  
  7 purchase totals = $862.36       $935.0143   $935.01   $935.05   $935.00