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 $186.43   6.119%   $197.8377   $197.84   $197.85   $197.80  
  Purchase #2 $69.64   6.206%   $73.9619   $73.96   $73.95   $74.00  
  Purchase #3 $51.66   6.843%   $55.1951   $55.20   $55.20   $55.20  
  Purchase #4 $194.78   6.269%   $206.9908   $206.99   $207.00   $207.00  
  Purchase #5 $8.29   4.781%   $8.6863   $8.69   $8.70   $8.70  
  Purchase #6 $239.79   4.644%   $250.9258   $250.93   $250.95   $250.90  
  Purchase #7 $54.35   13.474%   $61.6731   $61.67   $61.65   $61.70  
  7 purchase totals = $804.94       $855.2707   $855.28   $855.30   $855.30