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 $165.92   6.271%   $176.3248   $176.32   $176.30   $176.30  
  Purchase #2 $146.86   13.612%   $166.8506   $166.85   $166.85   $166.90  
  Purchase #3 $31.78   4.132%   $33.0931   $33.09   $33.10   $33.10  
  Purchase #4 $236.55   8.687%   $257.0991   $257.10   $257.10   $257.10  
  Purchase #5 $196.51   9.340%   $214.864   $214.86   $214.85   $214.90  
  Purchase #6 $224.30   10.816%   $248.5603   $248.56   $248.55   $248.60  
  Purchase #7 $152.43   4.569%   $159.3945   $159.39   $159.40   $159.40  
  7 purchase totals = $1,154.35       $1,256.1864   $1,256.17   $1,256.15   $1,256.30