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 $52.95   7.627%   $56.9885   $56.99   $57.00   $57.00  
  Purchase #2 $84.47   10.447%   $93.2946   $93.29   $93.30   $93.30  
  Purchase #3 $25.57   6.758%   $27.298   $27.30   $27.30   $27.30  
  Purchase #4 $93.83   6.198%   $99.6456   $99.65   $99.65   $99.60  
  Purchase #5 $182.51   13.166%   $206.5393   $206.54   $206.55   $206.50  
  Purchase #6 $109.78   4.136%   $114.3205   $114.32   $114.30   $114.30  
  Purchase #7 $188.53   11.656%   $210.5051   $210.51   $210.50   $210.50  
  7 purchase totals = $737.64       $808.5916   $808.60   $808.60   $808.50