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 $205.36   10.452%   $226.8242   $226.82   $226.80   $226.80  
  Purchase #2 $170.87   9.105%   $186.4277   $186.43   $186.45   $186.40  
  Purchase #3 $15.79   6.568%   $16.8271   $16.83   $16.85   $16.80  
  Purchase #4 $91.48   4.141%   $95.2682   $95.27   $95.25   $95.30  
  Purchase #5 $18.85   9.387%   $20.6194   $20.62   $20.60   $20.60  
  Purchase #6 $198.33   12.521%   $223.1629   $223.16   $223.15   $223.20  
  Purchase #7 $247.46   11.365%   $275.5838   $275.58   $275.60   $275.60  
  7 purchase totals = $948.14       $1,044.7133   $1,044.71   $1,044.70   $1,044.70