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 $241.57   9.234%   $263.8766   $263.88   $263.90   $263.90  
  Purchase #2 $186.26   5.191%   $195.9288   $195.93   $195.95   $195.90  
  Purchase #3 $216.80   7.336%   $232.7044   $232.70   $232.70   $232.70  
  Purchase #4 $217.76   7.381%   $233.8329   $233.83   $233.85   $233.80  
  Purchase #5 $101.73   7.790%   $109.6548   $109.65   $109.65   $109.70  
  Purchase #6 $151.61   6.844%   $161.9862   $161.99   $162.00   $162.00  
  Purchase #7 $123.82   13.244%   $140.2187   $140.22   $140.20   $140.20  
  7 purchase totals = $1,239.55       $1,338.2024   $1,338.20   $1,338.25   $1,338.20