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	$143.83	12.823%	$162.2733	$162.27	$162.25	$162.30
Purchase #2	$195.43	6.597%	$208.3225	$208.32	$208.30	$208.30
Purchase #3	$109.79	9.633%	$120.3661	$120.37	$120.35	$120.40
Purchase #4	$242.70	10.419%	$267.9869	$267.99	$268.00	$268.00
Purchase #5	$25.92	9.322%	$28.3363	$28.34	$28.35	$28.30
Purchase #6	$174.32	12.659%	$196.3872	$196.39	$196.40	$196.40
Purchase #7	$16.35	12.853%	$18.4515	$18.45	$18.45	$18.50
7 purchase totals =	$908.34		$1,002.1238	$1,002.13	$1,002.10	$1,002.20