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	$52.80	12.320%	$59.305	$59.31	$59.30	$59.30
Purchase #2	$168.55	8.306%	$182.5498	$182.55	$182.55	$182.50
Purchase #3	$86.57	5.543%	$91.3686	$91.37	$91.35	$91.40
Purchase #4	$115.96	13.187%	$131.2516	$131.25	$131.25	$131.30
Purchase #5	$148.73	11.194%	$165.3788	$165.38	$165.40	$165.40
Purchase #6	$142.63	5.110%	$149.9184	$149.92	$149.90	$149.90
Purchase #7	$46.68	8.521%	$50.6576	$50.66	$50.65	$50.70
7 purchase totals =	$761.92		$830.4298	$830.44	$830.40	$830.50