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	$152.73	8.796%	$166.1641	$166.16	$166.15	$166.20
Purchase #2	$212.51	11.106%	$236.1114	$236.11	$236.10	$236.10
Purchase #3	$55.33	7.665%	$59.571	$59.57	$59.55	$59.60
Purchase #4	$54.48	6.379%	$57.9553	$57.96	$57.95	$58.00
Purchase #5	$13.65	8.277%	$14.7798	$14.78	$14.80	$14.80
Purchase #6	$83.84	6.234%	$89.0666	$89.07	$89.05	$89.10
Purchase #7	$148.74	5.290%	$156.6083	$156.61	$156.60	$156.60
7 purchase totals =	$721.28		$780.2565	$780.26	$780.20	$780.40