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 $68.43   10.588%   $75.6754   $75.68   $75.70   $75.70  
  Purchase #2 $24.33   9.748%   $26.7017   $26.70   $26.70   $26.70  
  Purchase #3 $96.63   5.551%   $101.9939   $101.99   $102.00   $102.00  
  Purchase #4 $114.45   11.272%   $127.3508   $127.35   $127.35   $127.40  
  Purchase #5 $162.78   9.504%   $178.2506   $178.25   $178.25   $178.30  
  Purchase #6 $170.74   11.767%   $190.831   $190.83   $190.85   $190.80  
  Purchase #7 $209.76   12.784%   $236.5757   $236.58   $236.60   $236.60  
  7 purchase totals = $847.12       $937.3791   $937.38   $937.45   $937.50