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 $242.61   10.461%   $267.9894   $267.99   $268.00   $268.00  
  Purchase #2 $113.29   9.761%   $124.3482   $124.35   $124.35   $124.30  
  Purchase #3 $85.94   9.139%   $93.7941   $93.79   $93.80   $93.80  
  Purchase #4 $171.27   3.398%   $177.0898   $177.09   $177.10   $177.10  
  Purchase #5 $142.76   3.847%   $148.252   $148.25   $148.25   $148.30  
  Purchase #6 $52.90   10.869%   $58.6497   $58.65   $58.65   $58.60  
  Purchase #7 $226.94   10.866%   $251.5993   $251.60   $251.60   $251.60  
  7 purchase totals = $1,035.71       $1,121.7225   $1,121.72   $1,121.75   $1,121.70