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 $188.57   6.802%   $201.3965   $201.40   $201.40   $201.40  
  Purchase #2 $80.89   6.307%   $85.9917   $85.99   $86.00   $86.00  
  Purchase #3 $133.57   10.454%   $147.5334   $147.53   $147.55   $147.50  
  Purchase #4 $168.32   5.521%   $177.6129   $177.61   $177.60   $177.60  
  Purchase #5 $58.53   12.233%   $65.69   $65.69   $65.70   $65.70  
  Purchase #6 $58.40   3.797%   $60.6174   $60.62   $60.60   $60.60  
  Purchase #7 $161.29   13.759%   $183.4819   $183.48   $183.50   $183.50  
  7 purchase totals = $849.57       $922.3238   $922.32   $922.35   $922.30