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 $247.95   6.804%   $264.8205   $264.82   $264.80   $264.80  
  Purchase #2 $188.65   13.192%   $213.5367   $213.54   $213.55   $213.50  
  Purchase #3 $74.83   13.337%   $84.8101   $84.81   $84.80   $84.80  
  Purchase #4 $182.38   6.216%   $193.7167   $193.72   $193.70   $193.70  
  Purchase #5 $122.95   5.216%   $129.3631   $129.36   $129.35   $129.40  
  Purchase #6 $96.96   3.501%   $100.3546   $100.35   $100.35   $100.40  
  Purchase #7 $63.61   8.254%   $68.8604   $68.86   $68.85   $68.90  
  7 purchase totals = $977.33       $1,055.4621   $1,055.46   $1,055.40   $1,055.50