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 $117.67   9.867%   $129.2805   $129.28   $129.30   $129.30  
  Purchase #2 $203.90   6.833%   $217.8325   $217.83   $217.85   $217.80  
  Purchase #3 $30.27   6.853%   $32.3444   $32.34   $32.35   $32.30  
  Purchase #4 $184.66   5.598%   $194.9973   $195.00   $195.00   $195.00  
  Purchase #5 $37.64   9.483%   $41.2094   $41.21   $41.20   $41.20  
  Purchase #6 $212.27   10.617%   $234.8067   $234.81   $234.80   $234.80  
  Purchase #7 $243.38   7.735%   $262.2054   $262.21   $262.20   $262.20  
  7 purchase totals = $1,029.79       $1,112.6762   $1,112.68   $1,112.70   $1,112.60