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 $61.47   9.249%   $67.1554   $67.16   $67.15   $67.20  
  Purchase #2 $239.95   7.459%   $257.8479   $257.85   $257.85   $257.80  
  Purchase #3 $68.67   3.537%   $71.0989   $71.10   $71.10   $71.10  
  Purchase #4 $14.63   12.816%   $16.505   $16.51   $16.50   $16.50  
  Purchase #5 $123.46   6.705%   $131.738   $131.74   $131.75   $131.70  
  Purchase #6 $156.33   8.847%   $170.1605   $170.16   $170.15   $170.20  
  Purchase #7 $243.94   10.492%   $269.5342   $269.53   $269.55   $269.50  
  7 purchase totals = $908.45       $984.0399   $984.05   $984.05   $984.00