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 $232.62   6.464%   $247.6566   $247.66   $247.65   $247.70  
  Purchase #2 $182.26   8.460%   $197.6792   $197.68   $197.70   $197.70  
  Purchase #3 $169.91   9.195%   $185.5332   $185.53   $185.55   $185.50  
  Purchase #4 $115.55   13.535%   $131.1897   $131.19   $131.20   $131.20  
  Purchase #5 $68.94   10.315%   $76.0512   $76.05   $76.05   $76.10  
  Purchase #6 $54.56   13.637%   $62.0003   $62.00   $62.00   $62.00  
  Purchase #7 $140.42   8.664%   $152.586   $152.59   $152.60   $152.60  
  7 purchase totals = $964.26       $1,052.6962   $1,052.70   $1,052.75   $1,052.80