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 $125.98   10.391%   $139.0706   $139.07   $139.05   $139.10  
  Purchase #2 $142.37   3.487%   $147.3344   $147.33   $147.35   $147.30  
  Purchase #3 $90.95   8.362%   $98.5552   $98.56   $98.55   $98.60  
  Purchase #4 $151.58   13.103%   $171.4415   $171.44   $171.45   $171.40  
  Purchase #5 $241.37   13.755%   $274.5704   $274.57   $274.55   $274.60  
  Purchase #6 $169.66   10.132%   $186.85   $186.85   $186.85   $186.90  
  Purchase #7 $16.30   9.299%   $17.8157   $17.82   $17.80   $17.80  
  7 purchase totals = $938.21       $1,035.6378   $1,035.64   $1,035.60   $1,035.70