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 $69.83   8.226%   $75.5742   $75.57   $75.55   $75.60  
  Purchase #2 $13.38   8.850%   $14.5641   $14.56   $14.55   $14.60  
  Purchase #3 $189.47   5.826%   $200.5085   $200.51   $200.50   $200.50  
  Purchase #4 $248.78   9.440%   $272.2648   $272.26   $272.25   $272.30  
  Purchase #5 $247.76   3.388%   $256.1541   $256.15   $256.15   $256.20  
  Purchase #6 $20.80   10.797%   $23.0458   $23.05   $23.05   $23.00  
  Purchase #7 $195.73   8.566%   $212.4962   $212.50   $212.50   $212.50  
  7 purchase totals = $985.75       $1,054.6077   $1,054.60   $1,054.55   $1,054.70