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 $217.74   13.356%   $246.8214   $246.82   $246.80   $246.80  
  Purchase #2 $130.95   12.250%   $146.9914   $146.99   $147.00   $147.00  
  Purchase #3 $54.28   7.526%   $58.3651   $58.37   $58.35   $58.40  
  Purchase #4 $217.90   7.634%   $234.5345   $234.53   $234.55   $234.50  
  Purchase #5 $223.73   12.842%   $252.4614   $252.46   $252.45   $252.50  
  Purchase #6 $67.29   3.861%   $69.8881   $69.89   $69.90   $69.90  
  Purchase #7 $242.87   4.147%   $252.9418   $252.94   $252.95   $252.90  
  7 purchase totals = $1,154.76       $1,262.0037   $1,262.00   $1,262.00   $1,262.00