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 $136.46   10.720%   $151.0885   $151.09   $151.10   $151.10  
  Purchase #2 $245.72   11.442%   $273.8353   $273.84   $273.85   $273.80  
  Purchase #3 $163.52   12.682%   $184.2576   $184.26   $184.25   $184.30  
  Purchase #4 $69.29   5.163%   $72.8674   $72.87   $72.85   $72.90  
  Purchase #5 $82.54   10.432%   $91.1506   $91.15   $91.15   $91.20  
  Purchase #6 $78.65   11.629%   $87.7962   $87.80   $87.80   $87.80  
  Purchase #7 $150.79   10.724%   $166.9607   $166.96   $166.95   $167.00  
  7 purchase totals = $926.97       $1,027.9563   $1,027.97   $1,027.95   $1,028.10