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 $239.58   11.416%   $266.9305   $266.93   $266.95   $266.90  
  Purchase #2 $226.65   9.224%   $247.5562   $247.56   $247.55   $247.60  
  Purchase #3 $95.57   5.297%   $100.6323   $100.63   $100.65   $100.60  
  Purchase #4 $230.61   6.744%   $246.1623   $246.16   $246.15   $246.20  
  Purchase #5 $122.50   12.136%   $137.3666   $137.37   $137.35   $137.40  
  Purchase #6 $13.58   7.441%   $14.5905   $14.59   $14.60   $14.60  
  Purchase #7 $133.93   5.246%   $140.956   $140.96   $140.95   $141.00  
  7 purchase totals = $1,062.42       $1,154.1944   $1,154.20   $1,154.20   $1,154.30