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 $44.34   6.109%   $47.0487   $47.05   $47.05   $47.00  
  Purchase #2 $216.64   7.712%   $233.3473   $233.35   $233.35   $233.30  
  Purchase #3 $160.87   4.503%   $168.114   $168.11   $168.10   $168.10  
  Purchase #4 $189.64   4.781%   $198.7067   $198.71   $198.70   $198.70  
  Purchase #5 $126.44   10.224%   $139.3672   $139.37   $139.35   $139.40  
  Purchase #6 $54.87   9.268%   $59.9554   $59.96   $59.95   $60.00  
  Purchase #7 $48.34   4.848%   $50.6835   $50.68   $50.70   $50.70  
  7 purchase totals = $841.14       $897.2228   $897.23   $897.20   $897.20