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	$34.56	12.563%	$38.9018	$38.90	$38.90	$38.90
Purchase #2	$234.61	11.751%	$262.179	$262.18	$262.20	$262.20
Purchase #3	$184.48	3.123%	$190.2413	$190.24	$190.25	$190.20
Purchase #4	$75.36	12.200%	$84.5539	$84.55	$84.55	$84.60
Purchase #5	$225.30	3.559%	$233.3184	$233.32	$233.30	$233.30
Purchase #6	$188.30	5.419%	$198.504	$198.50	$198.50	$198.50
Purchase #7	$104.33	6.595%	$111.2106	$111.21	$111.20	$111.20
7 purchase totals =	$1,046.94		$1,118.9090	$1,118.90	$1,118.90	$1,118.90