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 $7.41   11.584%   $8.2684   $8.27   $8.25   $8.30  
  Purchase #2 $115.73   3.374%   $119.6347   $119.63   $119.65   $119.60  
  Purchase #3 $157.80   13.461%   $179.0415   $179.04   $179.05   $179.00  
  Purchase #4 $32.36   4.870%   $33.9359   $33.94   $33.95   $33.90  
  Purchase #5 $243.74   9.536%   $266.983   $266.98   $267.00   $267.00  
  Purchase #6 $200.79   12.171%   $225.2282   $225.23   $225.25   $225.20  
  Purchase #7 $46.54   11.696%   $51.9833   $51.98   $52.00   $52.00  
  7 purchase totals = $804.37       $885.0750   $885.07   $885.15   $885.00