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	$37.55	11.803%	$41.982	$41.98	$42.00	$42.00
Purchase #2	$233.92	6.515%	$249.1599	$249.16	$249.15	$249.20
Purchase #3	$50.88	6.410%	$54.1414	$54.14	$54.15	$54.10
Purchase #4	$60.99	10.742%	$67.5415	$67.54	$67.55	$67.50
Purchase #5	$152.59	13.614%	$173.3636	$173.36	$173.35	$173.40
Purchase #6	$102.90	8.735%	$111.8883	$111.89	$111.90	$111.90
Purchase #7	$184.86	6.608%	$197.0755	$197.08	$197.10	$197.10
7 purchase totals =	$823.69		$895.1522	$895.15	$895.20	$895.20