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 $235.79   4.661%   $246.7802   $246.78   $246.80   $246.80  
  Purchase #2 $104.42   9.370%   $114.2042   $114.20   $114.20   $114.20  
  Purchase #3 $7.64   12.802%   $8.6181   $8.62   $8.60   $8.60  
  Purchase #4 $54.79   10.318%   $60.4432   $60.44   $60.45   $60.40  
  Purchase #5 $189.77   9.106%   $207.0505   $207.05   $207.05   $207.10  
  Purchase #6 $176.83   13.169%   $200.1167   $200.12   $200.10   $200.10  
  Purchase #7 $195.79   7.498%   $210.4703   $210.47   $210.45   $210.50  
  7 purchase totals = $965.03       $1,047.6832   $1,047.68   $1,047.65   $1,047.70