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	$200.40	12.654%	$225.7586	$225.76	$225.75	$225.80
Purchase #2	$49.45	10.661%	$54.7219	$54.72	$54.70	$54.70
Purchase #3	$186.81	10.320%	$206.0888	$206.09	$206.10	$206.10
Purchase #4	$182.61	4.499%	$190.8256	$190.83	$190.85	$190.80
Purchase #5	$184.40	10.580%	$203.9095	$203.91	$203.90	$203.90
Purchase #6	$204.96	9.842%	$225.1322	$225.13	$225.15	$225.10
Purchase #7	$79.56	3.436%	$82.2937	$82.29	$82.30	$82.30
7 purchase totals =	$1,088.19		$1,188.7303	$1,188.73	$1,188.75	$1,188.70