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	$92.43	6.229%	$98.1875	$98.19	$98.20	$98.20
Purchase #2	$80.83	11.576%	$90.1869	$90.19	$90.20	$90.20
Purchase #3	$106.36	5.608%	$112.3247	$112.32	$112.30	$112.30
Purchase #4	$154.57	7.466%	$166.1102	$166.11	$166.10	$166.10
Purchase #5	$152.51	8.401%	$165.3224	$165.32	$165.30	$165.30
Purchase #6	$53.27	12.442%	$59.8979	$59.90	$59.90	$59.90
Purchase #7	$235.63	12.202%	$264.3816	$264.38	$264.40	$264.40
7 purchase totals =	$875.60		$956.4112	$956.41	$956.40	$956.40