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	$90.73	12.236%	$101.8317	$101.83	$101.85	$101.80
Purchase #2	$123.37	4.146%	$128.4849	$128.48	$128.50	$128.50
Purchase #3	$244.82	3.508%	$253.4083	$253.41	$253.40	$253.40
Purchase #4	$202.25	10.260%	$223.0009	$223.00	$223.00	$223.00
Purchase #5	$62.80	4.221%	$65.4508	$65.45	$65.45	$65.50
Purchase #6	$82.25	8.821%	$89.5053	$89.51	$89.50	$89.50
Purchase #7	$230.42	12.594%	$259.4391	$259.44	$259.45	$259.40
7 purchase totals =	$1,036.64		$1,121.1210	$1,121.12	$1,121.15	$1,121.10