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 $246.39   4.522%   $257.5318   $257.53   $257.55   $257.50  
  Purchase #2 $173.33   12.247%   $194.5577   $194.56   $194.55   $194.60  
  Purchase #3 $160.55   11.275%   $178.652   $178.65   $178.65   $178.70  
  Purchase #4 $90.75   9.487%   $99.3595   $99.36   $99.35   $99.40  
  Purchase #5 $58.57   3.227%   $60.4601   $60.46   $60.45   $60.50  
  Purchase #6 $179.83   10.268%   $198.2949   $198.29   $198.30   $198.30  
  Purchase #7 $197.82   8.335%   $214.3083   $214.31   $214.30   $214.30  
  7 purchase totals = $1,107.24       $1,203.1643   $1,203.16   $1,203.15   $1,203.30