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 $246.28   11.862%   $275.4937   $275.49   $275.50   $275.50  
  Purchase #2 $130.69   5.305%   $137.6231   $137.62   $137.60   $137.60  
  Purchase #3 $207.96   8.607%   $225.8591   $225.86   $225.85   $225.90  
  Purchase #4 $206.32   7.356%   $221.4969   $221.50   $221.50   $221.50  
  Purchase #5 $78.92   7.652%   $84.959   $84.96   $84.95   $85.00  
  Purchase #6 $165.56   4.398%   $172.8413   $172.84   $172.85   $172.80  
  Purchase #7 $167.60   11.443%   $186.7785   $186.78   $186.80   $186.80  
  7 purchase totals = $1,203.33       $1,305.0516   $1,305.05   $1,305.05   $1,305.10