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	$71.91	8.254%	$77.8455	$77.85	$77.85	$77.80
Purchase #2	$125.29	5.384%	$132.0356	$132.04	$132.05	$132.00
Purchase #3	$51.73	3.731%	$53.66	$53.66	$53.65	$53.70
Purchase #4	$185.94	13.614%	$211.2539	$211.25	$211.25	$211.30
Purchase #5	$90.35	10.603%	$99.9298	$99.93	$99.95	$99.90
Purchase #6	$56.39	3.862%	$58.5678	$58.57	$58.55	$58.60
Purchase #7	$30.25	12.214%	$33.9447	$33.94	$33.95	$33.90
7 purchase totals =	$611.86		$667.2373	$667.24	$667.25	$667.20