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 $105.39   11.704%   $117.7248   $117.72   $117.70   $117.70  
  Purchase #2 $233.47   12.406%   $262.4343   $262.43   $262.45   $262.40  
  Purchase #3 $56.62   8.355%   $61.3506   $61.35   $61.35   $61.40  
  Purchase #4 $50.92   8.802%   $55.402   $55.40   $55.40   $55.40  
  Purchase #5 $107.79   13.798%   $122.6629   $122.66   $122.65   $122.70  
  Purchase #6 $98.99   7.227%   $106.144   $106.14   $106.15   $106.10  
  Purchase #7 $24.64   12.750%   $27.7816   $27.78   $27.80   $27.80  
  7 purchase totals = $677.82       $753.5002   $753.48   $753.50   $753.50