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 $58.29   9.260%   $63.6877   $63.69   $63.70   $63.70  
  Purchase #2 $189.92   13.873%   $216.2676   $216.27   $216.25   $216.30  
  Purchase #3 $187.51   11.556%   $209.1787   $209.18   $209.20   $209.20  
  Purchase #4 $211.40   7.260%   $226.7476   $226.75   $226.75   $226.70  
  Purchase #5 $86.65   4.545%   $90.5882   $90.59   $90.60   $90.60  
  Purchase #6 $107.55   9.423%   $117.6844   $117.68   $117.70   $117.70  
  Purchase #7 $10.77   10.554%   $11.9067   $11.91   $11.90   $11.90  
  7 purchase totals = $852.09       $936.0609   $936.07   $936.10   $936.10