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 $208.56   10.712%   $230.9009   $230.90   $230.90   $230.90  
  Purchase #2 $121.92   6.360%   $129.6741   $129.67   $129.65   $129.70  
  Purchase #3 $157.74   4.218%   $164.3935   $164.39   $164.40   $164.40  
  Purchase #4 $249.65   3.232%   $257.7187   $257.72   $257.70   $257.70  
  Purchase #5 $235.33   12.624%   $265.0381   $265.04   $265.05   $265.00  
  Purchase #6 $41.26   10.811%   $45.7206   $45.72   $45.70   $45.70  
  Purchase #7 $191.93   4.855%   $201.2482   $201.25   $201.25   $201.20  
  7 purchase totals = $1,206.39       $1,294.6941   $1,294.69   $1,294.65   $1,294.60