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 $230.56   10.611%   $255.0247   $255.02   $255.00   $255.00  
  Purchase #2 $113.92   7.307%   $122.2441   $122.24   $122.25   $122.20  
  Purchase #3 $21.93   11.323%   $24.4131   $24.41   $24.40   $24.40  
  Purchase #4 $200.30   5.269%   $210.8538   $210.85   $210.85   $210.90  
  Purchase #5 $130.53   5.421%   $137.606   $137.61   $137.60   $137.60  
  Purchase #6 $131.26   9.613%   $143.878   $143.88   $143.90   $143.90  
  Purchase #7 $147.41   11.195%   $163.9125   $163.91   $163.90   $163.90  
  7 purchase totals = $975.91       $1,057.9322   $1,057.92   $1,057.90   $1,057.90