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 $93.37   11.848%   $104.4325   $104.43   $104.45   $104.40  
  Purchase #2 $239.39   12.485%   $269.2778   $269.28   $269.30   $269.30  
  Purchase #3 $248.58   11.257%   $276.5627   $276.56   $276.55   $276.60  
  Purchase #4 $226.47   8.853%   $246.5194   $246.52   $246.50   $246.50  
  Purchase #5 $76.51   8.828%   $83.2643   $83.26   $83.25   $83.30  
  Purchase #6 $66.74   9.598%   $73.1457   $73.15   $73.15   $73.10  
  Purchase #7 $102.76   9.266%   $112.2817   $112.28   $112.30   $112.30  
  7 purchase totals = $1,053.82       $1,165.4841   $1,165.48   $1,165.50   $1,165.50