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	$198.59	12.653%	$223.7176	$223.72	$223.70	$223.70
Purchase #2	$42.36	3.389%	$43.7956	$43.80	$43.80	$43.80
Purchase #3	$227.46	9.222%	$248.4364	$248.44	$248.45	$248.40
Purchase #4	$37.78	6.627%	$40.2837	$40.28	$40.30	$40.30
Purchase #5	$36.32	12.149%	$40.7325	$40.73	$40.75	$40.70
Purchase #6	$210.56	4.195%	$219.393	$219.39	$219.40	$219.40
Purchase #7	$28.79	5.802%	$30.4604	$30.46	$30.45	$30.50
7 purchase totals =	$781.86		$846.8192	$846.82	$846.85	$846.80