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	$96.77	7.624%	$104.1477	$104.15	$104.15	$104.10
Purchase #2	$117.46	11.140%	$130.545	$130.55	$130.55	$130.50
Purchase #3	$115.88	13.147%	$131.1147	$131.11	$131.10	$131.10
Purchase #4	$54.41	12.394%	$61.1536	$61.15	$61.15	$61.20
Purchase #5	$19.89	4.777%	$20.8401	$20.84	$20.85	$20.80
Purchase #6	$207.48	4.185%	$216.163	$216.16	$216.15	$216.20
Purchase #7	$187.98	9.553%	$205.9377	$205.94	$205.95	$205.90
7 purchase totals =	$799.87		$869.9018	$869.90	$869.90	$869.80