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 $176.47   11.810%   $197.3111   $197.31   $197.30   $197.30  
  Purchase #2 $185.91   4.159%   $193.642   $193.64   $193.65   $193.60  
  Purchase #3 $56.84   11.132%   $63.1674   $63.17   $63.15   $63.20  
  Purchase #4 $234.88   5.675%   $248.2094   $248.21   $248.20   $248.20  
  Purchase #5 $27.49   3.775%   $28.5277   $28.53   $28.55   $28.50  
  Purchase #6 $43.44   8.664%   $47.2036   $47.20   $47.20   $47.20  
  Purchase #7 $112.78   12.319%   $126.6734   $126.67   $126.65   $126.70  
  7 purchase totals = $837.81       $904.7346   $904.73   $904.70   $904.70