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 $200.97   3.479%   $207.9617   $207.96   $207.95   $208.00  
  Purchase #2 $60.48   5.468%   $63.787   $63.79   $63.80   $63.80  
  Purchase #3 $148.59   10.241%   $163.8071   $163.81   $163.80   $163.80  
  Purchase #4 $54.25   13.824%   $61.7495   $61.75   $61.75   $61.70  
  Purchase #5 $206.62   9.705%   $226.6725   $226.67   $226.65   $226.70  
  Purchase #6 $9.92   7.288%   $10.643   $10.64   $10.65   $10.60  
  Purchase #7 $173.56   8.702%   $188.6632   $188.66   $188.65   $188.70  
  7 purchase totals = $854.39       $923.2840   $923.28   $923.25   $923.30