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 $200.68   13.414%   $227.5992   $227.60   $227.60   $227.60  
  Purchase #2 $164.83   10.533%   $182.1915   $182.19   $182.20   $182.20  
  Purchase #3 $148.25   11.608%   $165.4589   $165.46   $165.45   $165.50  
  Purchase #4 $202.75   11.455%   $225.975   $225.98   $226.00   $226.00  
  Purchase #5 $39.70   11.610%   $44.3092   $44.31   $44.30   $44.30  
  Purchase #6 $153.50   6.578%   $163.5972   $163.60   $163.60   $163.60  
  Purchase #7 $226.62   8.655%   $246.234   $246.23   $246.25   $246.20  
  7 purchase totals = $1,136.33       $1,255.3650   $1,255.37   $1,255.40   $1,255.40