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 $17.32   13.663%   $19.6864   $19.69   $19.70   $19.70  
  Purchase #2 $66.30   3.800%   $68.8194   $68.82   $68.80   $68.80  
  Purchase #3 $242.81   4.260%   $253.1537   $253.15   $253.15   $253.20  
  Purchase #4 $39.40   7.657%   $42.4169   $42.42   $42.40   $42.40  
  Purchase #5 $174.25   4.220%   $181.6034   $181.60   $181.60   $181.60  
  Purchase #6 $96.57   4.386%   $100.8056   $100.81   $100.80   $100.80  
  Purchase #7 $20.70   3.869%   $21.5009   $21.50   $21.50   $21.50  
  7 purchase totals = $657.35       $687.9863   $687.99   $687.95   $688.00