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 $22.66   9.523%   $24.8179   $24.82   $24.80   $24.80  
  Purchase #2 $220.74   6.740%   $235.6179   $235.62   $235.60   $235.60  
  Purchase #3 $109.48   5.282%   $115.2627   $115.26   $115.25   $115.30  
  Purchase #4 $154.91   5.438%   $163.334   $163.33   $163.35   $163.30  
  Purchase #5 $196.86   3.664%   $204.073   $204.07   $204.05   $204.10  
  Purchase #6 $87.50   3.320%   $90.405   $90.41   $90.40   $90.40  
  Purchase #7 $126.87   12.238%   $142.3964   $142.40   $142.40   $142.40  
  7 purchase totals = $919.02       $975.9069   $975.91   $975.85   $975.90