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 $82.38   10.833%   $91.3042   $91.30   $91.30   $91.30  
  Purchase #2 $192.29   10.478%   $212.4381   $212.44   $212.45   $212.40  
  Purchase #3 $233.28   4.626%   $244.0715   $244.07   $244.05   $244.10  
  Purchase #4 $183.93   12.504%   $206.9286   $206.93   $206.95   $206.90  
  Purchase #5 $168.48   12.391%   $189.3564   $189.36   $189.35   $189.40  
  Purchase #6 $61.86   11.569%   $69.0166   $69.02   $69.00   $69.00  
  Purchase #7 $165.36   12.285%   $185.6745   $185.67   $185.65   $185.70  
  7 purchase totals = $1,087.58       $1,198.7899   $1,198.79   $1,198.75   $1,198.80