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 $173.45   12.304%   $194.7913   $194.79   $194.80   $194.80  
  Purchase #2 $55.56   4.804%   $58.2291   $58.23   $58.25   $58.20  
  Purchase #3 $167.48   4.772%   $175.4721   $175.47   $175.45   $175.50  
  Purchase #4 $113.82   9.686%   $124.8446   $124.84   $124.85   $124.80  
  Purchase #5 $67.45   13.779%   $76.7439   $76.74   $76.75   $76.70  
  Purchase #6 $49.82   7.593%   $53.6028   $53.60   $53.60   $53.60  
  Purchase #7 $65.40   6.647%   $69.7471   $69.75   $69.75   $69.70  
  7 purchase totals = $692.98       $753.4309   $753.42   $753.45   $753.30