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	$78.40	4.452%	$81.8904	$81.89	$81.90	$81.90
Purchase #2	$150.54	3.741%	$156.1717	$156.17	$156.15	$156.20
Purchase #3	$194.27	11.637%	$216.8772	$216.88	$216.90	$216.90
Purchase #4	$92.49	4.720%	$96.8555	$96.86	$96.85	$96.90
Purchase #5	$139.27	9.339%	$152.2764	$152.28	$152.30	$152.30
Purchase #6	$77.50	4.844%	$81.2541	$81.25	$81.25	$81.30
Purchase #7	$21.76	7.804%	$23.4582	$23.46	$23.45	$23.50
7 purchase totals =	$754.23		$808.7835	$808.79	$808.80	$809.00