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 $106.89   7.259%   $114.6491   $114.65   $114.65   $114.60  
  Purchase #2 $134.89   13.522%   $153.1298   $153.13   $153.15   $153.10  
  Purchase #3 $72.28   7.803%   $77.92   $77.92   $77.90   $77.90  
  Purchase #4 $129.64   3.202%   $133.7911   $133.79   $133.80   $133.80  
  Purchase #5 $187.88   8.215%   $203.3143   $203.31   $203.30   $203.30  
  Purchase #6 $128.35   4.201%   $133.742   $133.74   $133.75   $133.70  
  Purchase #7 $174.82   8.793%   $190.1919   $190.19   $190.20   $190.20  
  7 purchase totals = $934.75       $1,006.7382   $1,006.73   $1,006.75   $1,006.60