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 $240.82   3.461%   $249.1548   $249.15   $249.15   $249.20  
  Purchase #2 $219.41   6.200%   $233.0134   $233.01   $233.00   $233.00  
  Purchase #3 $80.46   13.450%   $91.2819   $91.28   $91.30   $91.30  
  Purchase #4 $116.60   10.566%   $128.92   $128.92   $128.90   $128.90  
  Purchase #5 $45.79   12.714%   $51.6117   $51.61   $51.60   $51.60  
  Purchase #6 $121.61   8.264%   $131.6599   $131.66   $131.65   $131.70  
  Purchase #7 $64.50   7.603%   $69.4039   $69.40   $69.40   $69.40  
  7 purchase totals = $889.19       $955.0456   $955.03   $955.00   $955.10