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	$250.27	10.227%	$275.8651	$275.87	$275.85	$275.90
Purchase #2	$209.87	4.811%	$219.9668	$219.97	$219.95	$220.00
Purchase #3	$47.54	11.408%	$52.9634	$52.96	$52.95	$53.00
Purchase #4	$24.27	3.642%	$25.1539	$25.15	$25.15	$25.20
Purchase #5	$141.87	12.434%	$159.5101	$159.51	$159.50	$159.50
Purchase #6	$77.92	9.682%	$85.4642	$85.46	$85.45	$85.50
Purchase #7	$218.92	9.109%	$238.8614	$238.86	$238.85	$238.90
7 purchase totals =	$970.66		$1,057.7849	$1,057.78	$1,057.70	$1,058.00