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 $248.95   6.246%   $264.4994   $264.50   $264.50   $264.50  
  Purchase #2 $193.99   3.611%   $200.995   $201.00   $201.00   $201.00  
  Purchase #3 $217.78   11.166%   $242.0973   $242.10   $242.10   $242.10  
  Purchase #4 $90.55   9.561%   $99.2075   $99.21   $99.20   $99.20  
  Purchase #5 $182.62   12.808%   $206.01   $206.01   $206.00   $206.00  
  Purchase #6 $205.38   12.582%   $231.2209   $231.22   $231.20   $231.20  
  Purchase #7 $109.62   3.324%   $113.2638   $113.26   $113.25   $113.30  
  7 purchase totals = $1,248.89       $1,357.2939   $1,357.30   $1,357.25   $1,357.30