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 $232.71   4.473%   $243.1191   $243.12   $243.10   $243.10  
  Purchase #2 $25.57   4.759%   $26.7869   $26.79   $26.80   $26.80  
  Purchase #3 $185.97   4.255%   $193.883   $193.88   $193.90   $193.90  
  Purchase #4 $108.92   5.544%   $114.9585   $114.96   $114.95   $115.00  
  Purchase #5 $49.83   7.536%   $53.5852   $53.59   $53.60   $53.60  
  Purchase #6 $64.36   11.787%   $71.9461   $71.95   $71.95   $71.90  
  Purchase #7 $126.96   10.112%   $139.7982   $139.80   $139.80   $139.80  
  7 purchase totals = $794.32       $844.0770   $844.09   $844.10   $844.10