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	$80.89	7.738%	$87.1493	$87.15	$87.15	$87.10
Purchase #2	$83.64	3.492%	$86.5607	$86.56	$86.55	$86.60
Purchase #3	$46.82	8.586%	$50.84	$50.84	$50.85	$50.80
Purchase #4	$37.33	13.686%	$42.439	$42.44	$42.45	$42.40
Purchase #5	$157.46	4.289%	$164.2135	$164.21	$164.20	$164.20
Purchase #6	$105.73	10.304%	$116.6244	$116.62	$116.60	$116.60
Purchase #7	$193.49	8.384%	$209.7122	$209.71	$209.70	$209.70
7 purchase totals =	$705.36		$757.5391	$757.53	$757.50	$757.40