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	$76.51	4.425%	$79.8956	$79.90	$79.90	$79.90
Purchase #2	$201.78	3.722%	$209.2903	$209.29	$209.30	$209.30
Purchase #3	$71.46	13.274%	$80.9456	$80.95	$80.95	$80.90
Purchase #4	$79.59	9.600%	$87.2306	$87.23	$87.25	$87.20
Purchase #5	$176.35	13.561%	$200.2648	$200.26	$200.25	$200.30
Purchase #6	$242.84	5.151%	$255.3487	$255.35	$255.35	$255.30
Purchase #7	$73.89	11.145%	$82.125	$82.13	$82.15	$82.10
7 purchase totals =	$922.42		$995.1006	$995.11	$995.15	$995.00