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 $75.37   11.151%   $83.7745   $83.77   $83.75   $83.80  
  Purchase #2 $238.93   11.573%   $266.5814   $266.58   $266.60   $266.60  
  Purchase #3 $44.46   4.580%   $46.4963   $46.50   $46.50   $46.50  
  Purchase #4 $119.91   3.300%   $123.867   $123.87   $123.85   $123.90  
  Purchase #5 $165.87   12.392%   $186.4246   $186.42   $186.40   $186.40  
  Purchase #6 $151.96   7.411%   $163.2218   $163.22   $163.20   $163.20  
  Purchase #7 $122.93   6.429%   $130.8332   $130.83   $130.85   $130.80  
  7 purchase totals = $919.43       $1,001.1988   $1,001.19   $1,001.15   $1,001.20