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	$37.53	8.316%	$40.651	$40.65	$40.65	$40.70
Purchase #2	$81.67	5.237%	$85.9471	$85.95	$85.95	$85.90
Purchase #3	$119.83	6.408%	$127.5087	$127.51	$127.50	$127.50
Purchase #4	$73.63	5.648%	$77.7886	$77.79	$77.80	$77.80
Purchase #5	$128.55	11.130%	$142.8576	$142.86	$142.85	$142.90
Purchase #6	$79.46	11.190%	$88.3516	$88.35	$88.35	$88.40
Purchase #7	$74.58	13.798%	$84.8705	$84.87	$84.85	$84.90
7 purchase totals =	$595.25		$647.9751	$647.98	$647.95	$648.10