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 $75.65   8.585%   $82.1446   $82.14   $82.15   $82.10  
  Purchase #2 $130.46   11.679%   $145.6964   $145.70   $145.70   $145.70  
  Purchase #3 $140.62   8.387%   $152.4138   $152.41   $152.40   $152.40  
  Purchase #4 $211.73   11.451%   $235.9752   $235.98   $236.00   $236.00  
  Purchase #5 $100.87   13.231%   $114.2161   $114.22   $114.20   $114.20  
  Purchase #6 $237.81   9.258%   $259.8264   $259.83   $259.85   $259.80  
  Purchase #7 $48.96   8.829%   $53.2827   $53.28   $53.30   $53.30  
  7 purchase totals = $946.10       $1,043.5552   $1,043.56   $1,043.60   $1,043.50