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 $194.87   6.822%   $208.164   $208.16   $208.15   $208.20  
  Purchase #2 $88.32   9.774%   $96.9524   $96.95   $96.95   $97.00  
  Purchase #3 $205.99   3.773%   $213.762   $213.76   $213.75   $213.80  
  Purchase #4 $154.29   4.679%   $161.5092   $161.51   $161.50   $161.50  
  Purchase #5 $129.90   3.866%   $134.9219   $134.92   $134.90   $134.90  
  Purchase #6 $132.44   7.767%   $142.7266   $142.73   $142.75   $142.70  
  Purchase #7 $41.70   3.342%   $43.0936   $43.09   $43.10   $43.10  
  7 purchase totals = $947.51       $1,001.1297   $1,001.12   $1,001.10   $1,001.20