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 $72.89   13.656%   $82.8439   $82.84   $82.85   $82.80  
  Purchase #2 $92.57   10.531%   $102.3185   $102.32   $102.30   $102.30  
  Purchase #3 $227.28   7.590%   $244.5306   $244.53   $244.55   $244.50  
  Purchase #4 $44.64   10.289%   $49.233   $49.23   $49.25   $49.20  
  Purchase #5 $245.51   6.111%   $260.5131   $260.51   $260.50   $260.50  
  Purchase #6 $124.71   4.288%   $130.0576   $130.06   $130.05   $130.10  
  Purchase #7 $106.50   6.225%   $113.1296   $113.13   $113.15   $113.10  
  7 purchase totals = $914.10       $982.6263   $982.62   $982.65   $982.50