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 $183.76   10.871%   $203.7365   $203.74   $203.75   $203.70  
  Purchase #2 $55.40   10.610%   $61.2779   $61.28   $61.30   $61.30  
  Purchase #3 $13.28   11.725%   $14.8371   $14.84   $14.85   $14.80  
  Purchase #4 $235.27   7.864%   $253.7716   $253.77   $253.75   $253.80  
  Purchase #5 $156.92   11.542%   $175.0317   $175.03   $175.05   $175.00  
  Purchase #6 $102.73   8.611%   $111.5761   $111.58   $111.60   $111.60  
  Purchase #7 $123.89   9.649%   $135.8441   $135.84   $135.85   $135.80  
  7 purchase totals = $871.25       $956.0750   $956.08   $956.15   $956.00