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 $227.72   8.298%   $246.6162   $246.62   $246.60   $246.60  
  Purchase #2 $171.95   13.152%   $194.5649   $194.56   $194.55   $194.60  
  Purchase #3 $200.90   5.170%   $211.2865   $211.29   $211.30   $211.30  
  Purchase #4 $220.56   12.105%   $247.2588   $247.26   $247.25   $247.30  
  Purchase #5 $181.81   6.795%   $194.164   $194.16   $194.15   $194.20  
  Purchase #6 $49.29   4.451%   $51.4839   $51.48   $51.50   $51.50  
  Purchase #7 $23.30   9.174%   $25.4375   $25.44   $25.45   $25.40  
  7 purchase totals = $1,075.53       $1,170.8118   $1,170.81   $1,170.80   $1,170.90