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 $236.78   12.390%   $266.117   $266.12   $266.10   $266.10  
  Purchase #2 $176.40   11.784%   $197.187   $197.19   $197.20   $197.20  
  Purchase #3 $60.46   12.569%   $68.0592   $68.06   $68.05   $68.10  
  Purchase #4 $158.30   4.681%   $165.71   $165.71   $165.70   $165.70  
  Purchase #5 $147.73   12.615%   $166.3661   $166.37   $166.35   $166.40  
  Purchase #6 $7.74   6.667%   $8.256   $8.26   $8.25   $8.30  
  Purchase #7 $68.70   5.709%   $72.6221   $72.62   $72.60   $72.60  
  7 purchase totals = $856.11       $944.3174   $944.33   $944.25   $944.40