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	$72.61	9.380%	$79.4208	$79.42	$79.40	$79.40
Purchase #2	$143.58	4.501%	$150.0425	$150.04	$150.05	$150.00
Purchase #3	$130.79	4.345%	$136.4728	$136.47	$136.45	$136.50
Purchase #4	$224.45	13.577%	$254.9236	$254.92	$254.90	$254.90
Purchase #5	$82.88	9.533%	$90.781	$90.78	$90.80	$90.80
Purchase #6	$203.68	12.696%	$229.5392	$229.54	$229.55	$229.50
Purchase #7	$81.58	9.812%	$89.5846	$89.58	$89.60	$89.60
7 purchase totals =	$939.57		$1,030.7645	$1,030.75	$1,030.75	$1,030.70