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 $173.96   10.779%   $192.7111   $192.71   $192.70   $192.70  
  Purchase #2 $205.37   9.767%   $225.4285   $225.43   $225.45   $225.40  
  Purchase #3 $181.96   4.733%   $190.5722   $190.57   $190.55   $190.60  
  Purchase #4 $245.69   13.454%   $278.7451   $278.75   $278.75   $278.70  
  Purchase #5 $212.31   4.123%   $221.0635   $221.06   $221.05   $221.10  
  Purchase #6 $41.94   11.521%   $46.7719   $46.77   $46.75   $46.80  
  Purchase #7 $58.55   7.858%   $63.1509   $63.15   $63.15   $63.20  
  7 purchase totals = $1,119.78       $1,218.4432   $1,218.44   $1,218.40   $1,218.50