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 $105.55   12.646%   $118.8979   $118.90   $118.90   $118.90  
  Purchase #2 $77.65   8.757%   $84.4498   $84.45   $84.45   $84.40  
  Purchase #3 $68.26   9.600%   $74.813   $74.81   $74.80   $74.80  
  Purchase #4 $49.62   13.747%   $56.4413   $56.44   $56.45   $56.40  
  Purchase #5 $89.79   6.802%   $95.8975   $95.90   $95.90   $95.90  
  Purchase #6 $198.92   6.189%   $211.2312   $211.23   $211.25   $211.20  
  Purchase #7 $73.48   10.242%   $81.0058   $81.01   $81.00   $81.00  
  7 purchase totals = $663.27       $722.7365   $722.74   $722.75   $722.60