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 $55.60   10.280%   $61.3157   $61.32   $61.30   $61.30  
  Purchase #2 $221.56   12.523%   $249.306   $249.31   $249.30   $249.30  
  Purchase #3 $59.88   5.185%   $62.9848   $62.98   $63.00   $63.00  
  Purchase #4 $42.91   10.720%   $47.51   $47.51   $47.50   $47.50  
  Purchase #5 $224.91   7.531%   $241.848   $241.85   $241.85   $241.80  
  Purchase #6 $185.99   9.306%   $203.2982   $203.30   $203.30   $203.30  
  Purchase #7 $130.85   3.277%   $135.138   $135.14   $135.15   $135.10  
  7 purchase totals = $921.70       $1,001.4007   $1,001.41   $1,001.40   $1,001.30