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 $48.27   13.271%   $54.6759   $54.68   $54.70   $54.70  
  Purchase #2 $96.68   12.583%   $108.8452   $108.85   $108.85   $108.80  
  Purchase #3 $11.50   5.759%   $12.1623   $12.16   $12.15   $12.20  
  Purchase #4 $50.96   5.505%   $53.7653   $53.77   $53.75   $53.80  
  Purchase #5 $156.82   7.141%   $168.0185   $168.02   $168.00   $168.00  
  Purchase #6 $243.29   6.190%   $258.3497   $258.35   $258.35   $258.30  
  Purchase #7 $192.89   4.621%   $201.8034   $201.80   $201.80   $201.80  
  7 purchase totals = $800.41       $857.6203   $857.63   $857.60   $857.60