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 $170.67   8.164%   $184.6035   $184.60   $184.60   $184.60  
  Purchase #2 $135.31   8.141%   $146.3256   $146.33   $146.35   $146.30  
  Purchase #3 $248.46   10.383%   $274.2576   $274.26   $274.25   $274.30  
  Purchase #4 $14.34   9.726%   $15.7347   $15.73   $15.75   $15.70  
  Purchase #5 $204.26   6.770%   $218.0884   $218.09   $218.10   $218.10  
  Purchase #6 $181.39   10.790%   $200.962   $200.96   $200.95   $201.00  
  Purchase #7 $208.85   13.307%   $236.6417   $236.64   $236.65   $236.60  
  7 purchase totals = $1,163.28       $1,276.6135   $1,276.61   $1,276.65   $1,276.60