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 $26.37   9.532%   $28.8836   $28.88   $28.90   $28.90  
  Purchase #2 $110.93   9.862%   $121.8699   $121.87   $121.85   $121.90  
  Purchase #3 $74.83   13.409%   $84.864   $84.86   $84.85   $84.90  
  Purchase #4 $177.95   8.734%   $193.4922   $193.49   $193.50   $193.50  
  Purchase #5 $227.25   6.218%   $241.3804   $241.38   $241.40   $241.40  
  Purchase #6 $105.66   9.754%   $115.9661   $115.97   $115.95   $116.00  
  Purchase #7 $152.58   3.334%   $157.667   $157.67   $157.65   $157.70  
  7 purchase totals = $875.57       $944.1232   $944.12   $944.10   $944.30