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 $182.72   13.148%   $206.744   $206.74   $206.75   $206.70  
  Purchase #2 $197.61   5.692%   $208.858   $208.86   $208.85   $208.90  
  Purchase #3 $185.78   10.472%   $205.2349   $205.23   $205.25   $205.20  
  Purchase #4 $65.42   7.866%   $70.5659   $70.57   $70.55   $70.60  
  Purchase #5 $52.97   5.357%   $55.8076   $55.81   $55.80   $55.80  
  Purchase #6 $193.50   9.588%   $212.0528   $212.05   $212.05   $212.10  
  Purchase #7 $104.50   6.316%   $111.1002   $111.10   $111.10   $111.10  
  7 purchase totals = $982.50       $1,070.3634   $1,070.36   $1,070.35   $1,070.40