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 $247.45   5.348%   $260.6836   $260.68   $260.70   $260.70  
  Purchase #2 $119.91   11.651%   $133.8807   $133.88   $133.90   $133.90  
  Purchase #3 $223.68   12.179%   $250.922   $250.92   $250.90   $250.90  
  Purchase #4 $160.42   10.492%   $177.2513   $177.25   $177.25   $177.30  
  Purchase #5 $187.68   3.194%   $193.6745   $193.67   $193.65   $193.70  
  Purchase #6 $30.80   3.333%   $31.8266   $31.83   $31.85   $31.80  
  Purchase #7 $33.39   11.578%   $37.2559   $37.26   $37.25   $37.30  
  7 purchase totals = $1,003.33       $1,085.4946   $1,085.49   $1,085.50   $1,085.60