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 $60.54   10.658%   $66.9924   $66.99   $67.00   $67.00  
  Purchase #2 $199.72   6.318%   $212.3383   $212.34   $212.35   $212.30  
  Purchase #3 $67.30   5.357%   $70.9053   $70.91   $70.90   $70.90  
  Purchase #4 $27.41   12.871%   $30.9379   $30.94   $30.95   $30.90  
  Purchase #5 $241.30   7.656%   $259.7739   $259.77   $259.75   $259.80  
  Purchase #6 $139.56   3.423%   $144.3371   $144.34   $144.35   $144.30  
  Purchase #7 $235.46   6.146%   $249.9314   $249.93   $249.95   $249.90  
  7 purchase totals = $971.29       $1,035.2163   $1,035.22   $1,035.25   $1,035.10