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 $225.90   7.713%   $243.3237   $243.32   $243.30   $243.30  
  Purchase #2 $63.94   13.169%   $72.3603   $72.36   $72.35   $72.40  
  Purchase #3 $13.96   5.185%   $14.6838   $14.68   $14.70   $14.70  
  Purchase #4 $118.91   4.341%   $124.0719   $124.07   $124.05   $124.10  
  Purchase #5 $178.89   12.283%   $200.8631   $200.86   $200.85   $200.90  
  Purchase #6 $208.62   12.185%   $234.0403   $234.04   $234.05   $234.00  
  Purchase #7 $23.55   4.495%   $24.6086   $24.61   $24.60   $24.60  
  7 purchase totals = $833.77       $913.9517   $913.94   $913.90   $914.00