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	$109.48	13.501%	$124.2609	$124.26	$124.25	$124.30
Purchase #2	$213.93	11.106%	$237.6891	$237.69	$237.70	$237.70
Purchase #3	$118.91	3.796%	$123.4238	$123.42	$123.40	$123.40
Purchase #4	$165.74	11.871%	$185.415	$185.42	$185.40	$185.40
Purchase #5	$69.89	12.647%	$78.729	$78.73	$78.75	$78.70
Purchase #6	$228.87	5.216%	$240.8079	$240.81	$240.80	$240.80
Purchase #7	$153.93	7.604%	$165.6348	$165.63	$165.65	$165.60
7 purchase totals =	$1,060.75		$1,155.9605	$1,155.96	$1,155.95	$1,155.90