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 $54.90   12.554%   $61.7921   $61.79   $61.80   $61.80  
  Purchase #2 $52.55   9.642%   $57.6169   $57.62   $57.60   $57.60  
  Purchase #3 $120.32   9.427%   $131.6626   $131.66   $131.65   $131.70  
  Purchase #4 $54.87   6.584%   $58.4826   $58.48   $58.50   $58.50  
  Purchase #5 $64.98   4.695%   $68.0308   $68.03   $68.05   $68.00  
  Purchase #6 $240.91   6.590%   $256.786   $256.79   $256.80   $256.80  
  Purchase #7 $45.30   4.851%   $47.4975   $47.50   $47.50   $47.50  
  7 purchase totals = $633.83       $681.8685   $681.87   $681.90   $681.90