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 $22.57   12.360%   $25.3597   $25.36   $25.35   $25.40  
  Purchase #2 $37.70   6.579%   $40.1803   $40.18   $40.20   $40.20  
  Purchase #3 $226.29   9.289%   $247.3101   $247.31   $247.30   $247.30  
  Purchase #4 $245.98   3.377%   $254.2867   $254.29   $254.30   $254.30  
  Purchase #5 $85.59   7.871%   $92.3268   $92.33   $92.35   $92.30  
  Purchase #6 $223.33   12.124%   $250.4065   $250.41   $250.40   $250.40  
  Purchase #7 $82.27   10.277%   $90.7249   $90.72   $90.70   $90.70  
  7 purchase totals = $923.73       $1,000.5950   $1,000.60   $1,000.60   $1,000.60