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 $44.94   6.598%   $47.9051   $47.91   $47.90   $47.90  
  Purchase #2 $71.49   4.856%   $74.9616   $74.96   $74.95   $75.00  
  Purchase #3 $114.89   11.165%   $127.7175   $127.72   $127.70   $127.70  
  Purchase #4 $38.87   10.653%   $43.0108   $43.01   $43.00   $43.00  
  Purchase #5 $50.59   3.352%   $52.2858   $52.29   $52.30   $52.30  
  Purchase #6 $173.41   5.416%   $182.8019   $182.80   $182.80   $182.80  
  Purchase #7 $216.85   13.323%   $245.7409   $245.74   $245.75   $245.70  
  7 purchase totals = $711.04       $774.4236   $774.43   $774.40   $774.40