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 $240.58   9.559%   $263.577   $263.58   $263.60   $263.60  
  Purchase #2 $97.83   8.221%   $105.8726   $105.87   $105.85   $105.90  
  Purchase #3 $17.54   12.621%   $19.7537   $19.75   $19.75   $19.80  
  Purchase #4 $114.31   11.609%   $127.5802   $127.58   $127.60   $127.60  
  Purchase #5 $182.98   7.643%   $196.9652   $196.97   $196.95   $197.00  
  Purchase #6 $102.29   13.525%   $116.1247   $116.12   $116.10   $116.10  
  Purchase #7 $23.42   13.527%   $26.588   $26.59   $26.60   $26.60  
  7 purchase totals = $778.95       $856.4614   $856.46   $856.45   $856.60