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 $68.99   4.624%   $72.1801   $72.18   $72.20   $72.20  
  Purchase #2 $71.55   7.492%   $76.9105   $76.91   $76.90   $76.90  
  Purchase #3 $153.66   9.623%   $168.4467   $168.45   $168.45   $168.40  
  Purchase #4 $125.69   11.828%   $140.5566   $140.56   $140.55   $140.60  
  Purchase #5 $80.96   4.513%   $84.6137   $84.61   $84.60   $84.60  
  Purchase #6 $200.39   5.408%   $211.2271   $211.23   $211.25   $211.20  
  Purchase #7 $186.99   5.484%   $197.2445   $197.24   $197.25   $197.20  
  7 purchase totals = $888.23       $951.1792   $951.18   $951.20   $951.10