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 $154.92   10.128%   $170.6103   $170.61   $170.60   $170.60  
  Purchase #2 $144.26   8.341%   $156.2927   $156.29   $156.30   $156.30  
  Purchase #3 $245.97   8.670%   $267.2956   $267.30   $267.30   $267.30  
  Purchase #4 $32.87   5.781%   $34.7702   $34.77   $34.75   $34.80  
  Purchase #5 $20.31   4.583%   $21.2408   $21.24   $21.25   $21.20  
  Purchase #6 $160.56   6.726%   $171.3593   $171.36   $171.35   $171.40  
  Purchase #7 $209.70   6.244%   $222.7937   $222.79   $222.80   $222.80  
  7 purchase totals = $968.59       $1,044.3626   $1,044.36   $1,044.35   $1,044.40