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 $36.98   12.706%   $41.6787   $41.68   $41.70   $41.70  
  Purchase #2 $196.83   5.348%   $207.3565   $207.36   $207.35   $207.40  
  Purchase #3 $216.93   11.214%   $241.2565   $241.26   $241.25   $241.30  
  Purchase #4 $184.83   12.518%   $207.967   $207.97   $207.95   $208.00  
  Purchase #5 $76.59   3.269%   $79.0937   $79.09   $79.10   $79.10  
  Purchase #6 $52.56   12.143%   $58.9424   $58.94   $58.95   $58.90  
  Purchase #7 $61.88   13.809%   $70.425   $70.43   $70.45   $70.40  
  7 purchase totals = $826.60       $906.7198   $906.73   $906.75   $906.80