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 $154.86   11.284%   $172.3344   $172.33   $172.35   $172.30  
  Purchase #2 $230.81   9.267%   $252.1992   $252.20   $252.20   $252.20  
  Purchase #3 $107.47   6.596%   $114.5587   $114.56   $114.55   $114.60  
  Purchase #4 $61.86   5.116%   $65.0248   $65.02   $65.00   $65.00  
  Purchase #5 $11.84   6.520%   $12.612   $12.61   $12.60   $12.60  
  Purchase #6 $244.89   12.319%   $275.058   $275.06   $275.05   $275.10  
  Purchase #7 $249.44   12.814%   $281.4032   $281.40   $281.40   $281.40  
  7 purchase totals = $1,061.17       $1,173.1903   $1,173.18   $1,173.15   $1,173.20