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 $185.85   4.211%   $193.6761   $193.68   $193.70   $193.70  
  Purchase #2 $129.87   8.826%   $141.3323   $141.33   $141.35   $141.30  
  Purchase #3 $236.73   3.316%   $244.58   $244.58   $244.60   $244.60  
  Purchase #4 $64.93   9.737%   $71.2522   $71.25   $71.25   $71.30  
  Purchase #5 $26.54   7.734%   $28.5926   $28.59   $28.60   $28.60  
  Purchase #6 $234.52   13.821%   $266.933   $266.93   $266.95   $266.90  
  Purchase #7 $195.98   9.849%   $215.2821   $215.28   $215.30   $215.30  
  7 purchase totals = $1,074.42       $1,161.6483   $1,161.64   $1,161.75   $1,161.70