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 $111.93   6.338%   $119.0241   $119.02   $119.00   $119.00  
  Purchase #2 $153.83   4.420%   $160.6293   $160.63   $160.65   $160.60  
  Purchase #3 $217.65   13.264%   $246.5191   $246.52   $246.50   $246.50  
  Purchase #4 $233.57   7.373%   $250.7911   $250.79   $250.80   $250.80  
  Purchase #5 $242.99   10.567%   $268.6668   $268.67   $268.65   $268.70  
  Purchase #6 $96.35   3.310%   $99.5392   $99.54   $99.55   $99.50  
  Purchase #7 $60.59   4.799%   $63.4977   $63.50   $63.50   $63.50  
  7 purchase totals = $1,116.91       $1,208.6673   $1,208.67   $1,208.65   $1,208.60