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 $245.83   8.858%   $267.6056   $267.61   $267.60   $267.60  
  Purchase #2 $177.41   9.216%   $193.7601   $193.76   $193.75   $193.80  
  Purchase #3 $206.63   9.822%   $226.9252   $226.93   $226.95   $226.90  
  Purchase #4 $195.99   10.635%   $216.8335   $216.83   $216.85   $216.80  
  Purchase #5 $42.48   6.716%   $45.333   $45.33   $45.35   $45.30  
  Purchase #6 $204.68   10.533%   $226.2389   $226.24   $226.25   $226.20  
  Purchase #7 $74.32   10.392%   $82.0433   $82.04   $82.05   $82.00  
  7 purchase totals = $1,147.34       $1,258.7396   $1,258.74   $1,258.80   $1,258.60