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 $195.57   8.166%   $211.5402   $211.54   $211.55   $211.50  
  Purchase #2 $96.59   8.608%   $104.9045   $104.90   $104.90   $104.90  
  Purchase #3 $141.83   5.837%   $150.1086   $150.11   $150.10   $150.10  
  Purchase #4 $68.29   9.382%   $74.697   $74.70   $74.70   $74.70  
  Purchase #5 $220.29   10.319%   $243.0217   $243.02   $243.00   $243.00  
  Purchase #6 $196.60   10.757%   $217.7483   $217.75   $217.75   $217.70  
  Purchase #7 $248.77   7.151%   $266.5595   $266.56   $266.55   $266.60  
  7 purchase totals = $1,167.94       $1,268.5798   $1,268.58   $1,268.55   $1,268.50