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 $70.91   11.422%   $79.0093   $79.01   $79.00   $79.00  
  Purchase #2 $136.98   11.674%   $152.971   $152.97   $152.95   $153.00  
  Purchase #3 $60.41   10.802%   $66.9355   $66.94   $66.95   $66.90  
  Purchase #4 $170.58   7.629%   $183.5935   $183.59   $183.60   $183.60  
  Purchase #5 $222.64   13.420%   $252.5183   $252.52   $252.50   $252.50  
  Purchase #6 $59.95   13.116%   $67.813   $67.81   $67.80   $67.80  
  Purchase #7 $241.94   13.312%   $274.1471   $274.15   $274.15   $274.10  
  7 purchase totals = $963.41       $1,076.9877   $1,076.99   $1,076.95   $1,076.90