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 $154.74   13.108%   $175.0233   $175.02   $175.00   $175.00  
  Purchase #2 $92.29   4.518%   $96.4597   $96.46   $96.45   $96.50  
  Purchase #3 $211.37   11.739%   $236.1827   $236.18   $236.20   $236.20  
  Purchase #4 $132.49   10.363%   $146.2199   $146.22   $146.20   $146.20  
  Purchase #5 $239.36   11.272%   $266.3407   $266.34   $266.35   $266.30  
  Purchase #6 $248.78   11.712%   $277.9171   $277.92   $277.90   $277.90  
  Purchase #7 $42.67   5.832%   $45.1585   $45.16   $45.15   $45.20  
  7 purchase totals = $1,121.70       $1,243.3019   $1,243.30   $1,243.25   $1,243.30