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 $242.96   11.117%   $269.9699   $269.97   $269.95   $270.00  
  Purchase #2 $145.26   10.721%   $160.8333   $160.83   $160.85   $160.80  
  Purchase #3 $139.68   3.331%   $144.3327   $144.33   $144.35   $144.30  
  Purchase #4 $161.90   11.856%   $181.0949   $181.09   $181.10   $181.10  
  Purchase #5 $236.53   7.788%   $254.951   $254.95   $254.95   $255.00  
  Purchase #6 $32.85   3.635%   $34.0441   $34.04   $34.05   $34.00  
  Purchase #7 $145.46   3.493%   $150.5409   $150.54   $150.55   $150.50  
  7 purchase totals = $1,104.64       $1,195.7668   $1,195.75   $1,195.80   $1,195.70