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 $61.68   5.803%   $65.2593   $65.26   $65.25   $65.30  
  Purchase #2 $11.34   10.488%   $12.5293   $12.53   $12.55   $12.50  
  Purchase #3 $189.56   4.232%   $197.5822   $197.58   $197.60   $197.60  
  Purchase #4 $234.59   5.243%   $246.8896   $246.89   $246.90   $246.90  
  Purchase #5 $80.44   13.665%   $91.4321   $91.43   $91.45   $91.40  
  Purchase #6 $79.57   4.126%   $82.8531   $82.85   $82.85   $82.90  
  Purchase #7 $7.58   13.615%   $8.612   $8.61   $8.60   $8.60  
  7 purchase totals = $664.76       $705.1576   $705.15   $705.20   $705.20