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 $198.83   5.279%   $209.3262   $209.33   $209.35   $209.30  
  Purchase #2 $146.39   12.442%   $164.6038   $164.60   $164.60   $164.60  
  Purchase #3 $63.99   9.426%   $70.0217   $70.02   $70.00   $70.00  
  Purchase #4 $118.34   10.423%   $130.6746   $130.67   $130.65   $130.70  
  Purchase #5 $15.95   8.217%   $17.2606   $17.26   $17.25   $17.30  
  Purchase #6 $98.74   3.746%   $102.4388   $102.44   $102.45   $102.40  
  Purchase #7 $58.63   6.208%   $62.2698   $62.27   $62.25   $62.30  
  7 purchase totals = $700.87       $756.5955   $756.59   $756.55   $756.60