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 $245.57   12.595%   $276.4995   $276.50   $276.50   $276.50  
  Purchase #2 $96.63   10.665%   $106.9356   $106.94   $106.95   $106.90  
  Purchase #3 $187.98   4.349%   $196.1553   $196.16   $196.15   $196.20  
  Purchase #4 $63.71   4.106%   $66.3259   $66.33   $66.35   $66.30  
  Purchase #5 $206.82   5.245%   $217.6677   $217.67   $217.65   $217.70  
  Purchase #6 $144.69   7.396%   $155.3913   $155.39   $155.40   $155.40  
  Purchase #7 $96.98   5.769%   $102.5748   $102.57   $102.55   $102.60  
  7 purchase totals = $1,042.38       $1,121.5501   $1,121.56   $1,121.55   $1,121.60