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 $95.83   9.207%   $104.6531   $104.65   $104.65   $104.70  
  Purchase #2 $88.28   3.267%   $91.1641   $91.16   $91.15   $91.20  
  Purchase #3 $158.37   11.442%   $176.4907   $176.49   $176.50   $176.50  
  Purchase #4 $247.45   9.684%   $271.4131   $271.41   $271.40   $271.40  
  Purchase #5 $195.77   11.434%   $218.1543   $218.15   $218.15   $218.20  
  Purchase #6 $60.78   6.198%   $64.5471   $64.55   $64.55   $64.50  
  Purchase #7 $13.33   8.439%   $14.4549   $14.45   $14.45   $14.50  
  7 purchase totals = $859.81       $940.8773   $940.86   $940.85   $941.00