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 $130.93   8.133%   $141.5785   $141.58   $141.60   $141.60  
  Purchase #2 $184.47   8.167%   $199.5357   $199.54   $199.55   $199.50  
  Purchase #3 $125.95   3.343%   $130.1605   $130.16   $130.15   $130.20  
  Purchase #4 $225.32   11.653%   $251.5765   $251.58   $251.60   $251.60  
  Purchase #5 $190.82   10.771%   $211.3732   $211.37   $211.35   $211.40  
  Purchase #6 $46.37   10.345%   $51.167   $51.17   $51.15   $51.20  
  Purchase #7 $26.45   8.637%   $28.7345   $28.73   $28.75   $28.70  
  7 purchase totals = $930.31       $1,014.1259   $1,014.13   $1,014.15   $1,014.20