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 $221.90   11.760%   $247.9954   $248.00   $248.00   $248.00  
  Purchase #2 $108.74   6.255%   $115.5417   $115.54   $115.55   $115.50  
  Purchase #3 $223.81   13.774%   $254.6376   $254.64   $254.65   $254.60  
  Purchase #4 $233.98   9.794%   $256.896   $256.90   $256.90   $256.90  
  Purchase #5 $60.87   13.463%   $69.0649   $69.06   $69.05   $69.10  
  Purchase #6 $234.60   4.862%   $246.0063   $246.01   $246.00   $246.00  
  Purchase #7 $215.92   12.762%   $243.4757   $243.48   $243.50   $243.50  
  7 purchase totals = $1,299.82       $1,433.6176   $1,433.63   $1,433.65   $1,433.60