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 $64.26   9.865%   $70.5992   $70.60   $70.60   $70.60  
  Purchase #2 $177.61   8.133%   $192.055   $192.06   $192.05   $192.10  
  Purchase #3 $138.26   13.112%   $156.3887   $156.39   $156.40   $156.40  
  Purchase #4 $246.59   3.784%   $255.921   $255.92   $255.90   $255.90  
  Purchase #5 $28.76   3.240%   $29.6918   $29.69   $29.70   $29.70  
  Purchase #6 $61.58   3.770%   $63.9016   $63.90   $63.90   $63.90  
  Purchase #7 $208.78   13.408%   $236.7732   $236.77   $236.75   $236.80  
  7 purchase totals = $925.84       $1,005.3305   $1,005.33   $1,005.30   $1,005.40