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 $150.83   8.632%   $163.8496   $163.85   $163.85   $163.80  
  Purchase #2 $92.38   12.608%   $104.0273   $104.03   $104.05   $104.00  
  Purchase #3 $224.43   10.288%   $247.5194   $247.52   $247.50   $247.50  
  Purchase #4 $224.61   12.527%   $252.7469   $252.75   $252.75   $252.70  
  Purchase #5 $32.89   8.705%   $35.7531   $35.75   $35.75   $35.80  
  Purchase #6 $188.83   4.245%   $196.8458   $196.85   $196.85   $196.80  
  Purchase #7 $19.99   4.485%   $20.8866   $20.89   $20.90   $20.90  
  7 purchase totals = $933.96       $1,021.6287   $1,021.64   $1,021.65   $1,021.50