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 $246.49   6.319%   $262.0657   $262.07   $262.05   $262.10  
  Purchase #2 $238.83   6.202%   $253.6422   $253.64   $253.65   $253.60  
  Purchase #3 $211.80   10.835%   $234.7485   $234.75   $234.75   $234.70  
  Purchase #4 $173.64   10.510%   $191.8896   $191.89   $191.90   $191.90  
  Purchase #5 $116.32   8.750%   $126.498   $126.50   $126.50   $126.50  
  Purchase #6 $124.56   6.322%   $132.4347   $132.43   $132.45   $132.40  
  Purchase #7 $59.38   10.869%   $65.834   $65.83   $65.85   $65.80  
  7 purchase totals = $1,171.02       $1,267.1127   $1,267.11   $1,267.15   $1,267.00