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 $60.64   4.103%   $63.1281   $63.13   $63.15   $63.10  
  Purchase #2 $128.86   8.390%   $139.6714   $139.67   $139.65   $139.70  
  Purchase #3 $23.27   7.750%   $25.0734   $25.07   $25.05   $25.10  
  Purchase #4 $153.42   3.308%   $158.4951   $158.50   $158.50   $158.50  
  Purchase #5 $80.28   9.220%   $87.6818   $87.68   $87.70   $87.70  
  Purchase #6 $219.61   13.214%   $248.6293   $248.63   $248.65   $248.60  
  Purchase #7 $218.33   4.382%   $227.8972   $227.90   $227.90   $227.90  
  7 purchase totals = $884.41       $950.5763   $950.58   $950.60   $950.60