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 $59.74   3.348%   $61.7401   $61.74   $61.75   $61.70  
  Purchase #2 $228.73   9.208%   $249.7915   $249.79   $249.80   $249.80  
  Purchase #3 $62.87   12.555%   $70.7633   $70.76   $70.75   $70.80  
  Purchase #4 $21.87   5.323%   $23.0341   $23.03   $23.05   $23.00  
  Purchase #5 $204.53   3.626%   $211.9463   $211.95   $211.95   $211.90  
  Purchase #6 $79.78   7.856%   $86.0475   $86.05   $86.05   $86.00  
  Purchase #7 $214.35   9.861%   $235.4871   $235.49   $235.50   $235.50  
  7 purchase totals = $871.87       $938.8099   $938.81   $938.85   $938.70