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 $59.33   3.616%   $61.4754   $61.48   $61.50   $61.50  
  Purchase #2 $66.29   13.830%   $75.4579   $75.46   $75.45   $75.50  
  Purchase #3 $117.78   12.565%   $132.5791   $132.58   $132.60   $132.60  
  Purchase #4 $73.97   5.361%   $77.9355   $77.94   $77.95   $77.90  
  Purchase #5 $98.32   13.204%   $111.3022   $111.30   $111.30   $111.30  
  Purchase #6 $173.29   10.626%   $191.7038   $191.70   $191.70   $191.70  
  Purchase #7 $246.79   8.609%   $268.0362   $268.04   $268.05   $268.00  
  7 purchase totals = $835.77       $918.4901   $918.50   $918.55   $918.50