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 $201.45   3.699%   $208.9016   $208.90   $208.90   $208.90  
  Purchase #2 $47.82   7.591%   $51.45   $51.45   $51.45   $51.50  
  Purchase #3 $239.36   13.495%   $271.6616   $271.66   $271.65   $271.70  
  Purchase #4 $23.65   3.663%   $24.5163   $24.52   $24.50   $24.50  
  Purchase #5 $212.77   7.588%   $228.915   $228.92   $228.90   $228.90  
  Purchase #6 $30.69   12.273%   $34.4566   $34.46   $34.45   $34.50  
  Purchase #7 $176.77   13.554%   $200.7294   $200.73   $200.75   $200.70  
  7 purchase totals = $932.51       $1,020.6305   $1,020.64   $1,020.60   $1,020.70