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 $206.76   13.718%   $235.1233   $235.12   $235.10   $235.10  
  Purchase #2 $58.33   3.655%   $60.462   $60.46   $60.45   $60.50  
  Purchase #3 $124.89   3.669%   $129.4722   $129.47   $129.45   $129.50  
  Purchase #4 $198.85   8.136%   $215.0284   $215.03   $215.05   $215.00  
  Purchase #5 $81.58   5.316%   $85.9168   $85.92   $85.90   $85.90  
  Purchase #6 $112.97   9.139%   $123.2943   $123.29   $123.30   $123.30  
  Purchase #7 $209.41   11.312%   $233.0985   $233.10   $233.10   $233.10  
  7 purchase totals = $992.79       $1,082.3955   $1,082.39   $1,082.35   $1,082.40