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 $203.47   13.555%   $231.0504   $231.05   $231.05   $231.10  
  Purchase #2 $44.62   4.806%   $46.7644   $46.76   $46.75   $46.80  
  Purchase #3 $163.48   7.123%   $175.1247   $175.12   $175.10   $175.10  
  Purchase #4 $107.99   3.146%   $111.3874   $111.39   $111.40   $111.40  
  Purchase #5 $160.41   11.384%   $178.6711   $178.67   $178.65   $178.70  
  Purchase #6 $164.78   4.782%   $172.6598   $172.66   $172.65   $172.70  
  Purchase #7 $216.99   13.193%   $245.6175   $245.62   $245.60   $245.60  
  7 purchase totals = $1,061.74       $1,161.2753   $1,161.27   $1,161.20   $1,161.40