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 $42.35   11.527%   $47.2317   $47.23   $47.25   $47.20  
  Purchase #2 $103.45   13.732%   $117.6558   $117.66   $117.65   $117.70  
  Purchase #3 $48.72   10.656%   $53.9116   $53.91   $53.90   $53.90  
  Purchase #4 $193.63   5.473%   $204.2274   $204.23   $204.25   $204.20  
  Purchase #5 $137.28   4.124%   $142.9414   $142.94   $142.95   $142.90  
  Purchase #6 $130.64   4.563%   $136.6011   $136.60   $136.60   $136.60  
  Purchase #7 $49.50   12.325%   $55.6009   $55.60   $55.60   $55.60  
  7 purchase totals = $705.57       $758.1699   $758.17   $758.20   $758.10