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 $111.65   7.106%   $119.5838   $119.58   $119.60   $119.60  
  Purchase #2 $173.72   4.285%   $181.1639   $181.16   $181.15   $181.20  
  Purchase #3 $250.34   3.760%   $259.7528   $259.75   $259.75   $259.80  
  Purchase #4 $16.76   3.783%   $17.394   $17.39   $17.40   $17.40  
  Purchase #5 $169.37   13.308%   $191.9098   $191.91   $191.90   $191.90  
  Purchase #6 $66.37   10.867%   $73.5824   $73.58   $73.60   $73.60  
  Purchase #7 $210.61   9.593%   $230.8138   $230.81   $230.80   $230.80  
  7 purchase totals = $998.82       $1,074.2005   $1,074.18   $1,074.20   $1,074.30