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 $116.27   13.288%   $131.72   $131.72   $131.70   $131.70  
  Purchase #2 $241.74   10.266%   $266.557   $266.56   $266.55   $266.60  
  Purchase #3 $165.45   9.389%   $180.9841   $180.98   $181.00   $181.00  
  Purchase #4 $189.57   3.193%   $195.623   $195.62   $195.60   $195.60  
  Purchase #5 $128.79   6.834%   $137.5915   $137.59   $137.60   $137.60  
  Purchase #6 $130.63   7.784%   $140.7982   $140.80   $140.80   $140.80  
  Purchase #7 $194.70   6.399%   $207.1589   $207.16   $207.15   $207.20  
  7 purchase totals = $1,167.15       $1,260.4327   $1,260.43   $1,260.40   $1,260.50