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 $231.82   5.402%   $244.3429   $244.34   $244.35   $244.30  
  Purchase #2 $26.86   3.222%   $27.7254   $27.73   $27.75   $27.70  
  Purchase #3 $23.27   11.609%   $25.9714   $25.97   $25.95   $26.00  
  Purchase #4 $168.66   9.208%   $184.1902   $184.19   $184.20   $184.20  
  Purchase #5 $135.83   4.207%   $141.5444   $141.54   $141.55   $141.50  
  Purchase #6 $70.70   13.717%   $80.3979   $80.40   $80.40   $80.40  
  Purchase #7 $39.69   3.233%   $40.9732   $40.97   $40.95   $41.00  
  7 purchase totals = $696.83       $745.1454   $745.14   $745.15   $745.10