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 $177.97   8.627%   $193.3235   $193.32   $193.30   $193.30  
  Purchase #2 $100.36   5.859%   $106.2401   $106.24   $106.25   $106.20  
  Purchase #3 $225.28   10.460%   $248.8443   $248.84   $248.85   $248.80  
  Purchase #4 $141.86   10.429%   $156.6546   $156.65   $156.65   $156.70  
  Purchase #5 $144.95   6.585%   $154.495   $154.50   $154.50   $154.50  
  Purchase #6 $236.90   6.576%   $252.4785   $252.48   $252.50   $252.50  
  Purchase #7 $67.32   10.405%   $74.3246   $74.32   $74.30   $74.30  
  7 purchase totals = $1,094.64       $1,186.3606   $1,186.35   $1,186.35   $1,186.30