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 $228.70   8.338%   $247.769   $247.77   $247.75   $247.80  
  Purchase #2 $7.95   7.138%   $8.5175   $8.52   $8.50   $8.50  
  Purchase #3 $81.95   6.389%   $87.1858   $87.19   $87.20   $87.20  
  Purchase #4 $59.83   4.584%   $62.5726   $62.57   $62.55   $62.60  
  Purchase #5 $200.72   7.531%   $215.8362   $215.84   $215.85   $215.80  
  Purchase #6 $157.70   10.609%   $174.4304   $174.43   $174.45   $174.40  
  Purchase #7 $24.82   6.825%   $26.514   $26.51   $26.50   $26.50  
  7 purchase totals = $761.67       $822.8255   $822.83   $822.80   $822.80