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	$85.73	5.191%	$90.1802	$90.18	$90.20	$90.20
Purchase #2	$246.89	3.400%	$255.2843	$255.28	$255.30	$255.30
Purchase #3	$159.27	7.668%	$171.4828	$171.48	$171.50	$171.50
Purchase #4	$238.26	4.260%	$248.4099	$248.41	$248.40	$248.40
Purchase #5	$146.94	9.846%	$161.4077	$161.41	$161.40	$161.40
Purchase #6	$169.79	7.517%	$182.5531	$182.55	$182.55	$182.60
Purchase #7	$111.55	12.500%	$125.4938	$125.49	$125.50	$125.50
7 purchase totals =	$1,158.43		$1,234.8118	$1,234.80	$1,234.85	$1,234.90