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	$221.68	5.420%	$233.6951	$233.70	$233.70	$233.70
Purchase #2	$42.61	7.677%	$45.8812	$45.88	$45.90	$45.90
Purchase #3	$48.99	12.360%	$55.0452	$55.05	$55.05	$55.00
Purchase #4	$89.47	7.155%	$95.8716	$95.87	$95.85	$95.90
Purchase #5	$152.69	12.507%	$171.7869	$171.79	$171.80	$171.80
Purchase #6	$209.90	10.262%	$231.4399	$231.44	$231.45	$231.40
Purchase #7	$99.80	6.308%	$106.0954	$106.10	$106.10	$106.10
7 purchase totals =	$865.14		$939.8153	$939.83	$939.85	$939.80