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	$96.61	3.687%	$100.172	$100.17	$100.15	$100.20
Purchase #2	$194.50	3.106%	$200.5412	$200.54	$200.55	$200.50
Purchase #3	$63.71	10.283%	$70.2613	$70.26	$70.25	$70.30
Purchase #4	$56.42	5.502%	$59.5242	$59.52	$59.50	$59.50
Purchase #5	$233.80	13.469%	$265.2905	$265.29	$265.30	$265.30
Purchase #6	$114.65	4.809%	$120.1635	$120.16	$120.15	$120.20
Purchase #7	$249.90	8.310%	$270.6667	$270.67	$270.65	$270.70
7 purchase totals =	$1,009.59		$1,086.6194	$1,086.61	$1,086.55	$1,086.70