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 $245.26   8.864%   $266.9998   $267.00   $267.00   $267.00  
  Purchase #2 $26.31   7.667%   $28.3272   $28.33   $28.35   $28.30  
  Purchase #3 $218.39   12.869%   $246.4946   $246.49   $246.50   $246.50  
  Purchase #4 $219.71   5.316%   $231.3898   $231.39   $231.40   $231.40  
  Purchase #5 $147.65   3.220%   $152.4043   $152.40   $152.40   $152.40  
  Purchase #6 $94.66   3.663%   $98.1274   $98.13   $98.15   $98.10  
  Purchase #7 $188.94   13.491%   $214.4299   $214.43   $214.45   $214.40  
  7 purchase totals = $1,140.92       $1,238.1730   $1,238.17   $1,238.25   $1,238.10