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 $228.86   11.197%   $254.4855   $254.49   $254.50   $254.50  
  Purchase #2 $140.45   10.146%   $154.7001   $154.70   $154.70   $154.70  
  Purchase #3 $122.63   3.817%   $127.3108   $127.31   $127.30   $127.30  
  Purchase #4 $66.34   5.441%   $69.9496   $69.95   $69.95   $69.90  
  Purchase #5 $153.70   8.686%   $167.0504   $167.05   $167.05   $167.10  
  Purchase #6 $196.97   6.151%   $209.0856   $209.09   $209.10   $209.10  
  Purchase #7 $87.91   12.821%   $99.1809   $99.18   $99.20   $99.20  
  7 purchase totals = $996.86       $1,081.7629   $1,081.77   $1,081.80   $1,081.80