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 $84.27   4.784%   $88.3015   $88.30   $88.30   $88.30  
  Purchase #2 $201.88   13.607%   $229.3498   $229.35   $229.35   $229.30  
  Purchase #3 $5.78   12.279%   $6.4897   $6.49   $6.50   $6.50  
  Purchase #4 $111.49   13.871%   $126.9548   $126.95   $126.95   $127.00  
  Purchase #5 $32.76   12.724%   $36.9284   $36.93   $36.95   $36.90  
  Purchase #6 $207.34   3.161%   $213.894   $213.89   $213.90   $213.90  
  Purchase #7 $218.43   10.598%   $241.5792   $241.58   $241.60   $241.60  
  7 purchase totals = $861.95       $943.4974   $943.49   $943.55   $943.50