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	$79.36	4.469%	$82.9066	$82.91	$82.90	$82.90
Purchase #2	$113.33	4.152%	$118.0355	$118.04	$118.05	$118.00
Purchase #3	$127.37	7.688%	$137.1622	$137.16	$137.15	$137.20
Purchase #4	$160.64	8.469%	$174.2446	$174.24	$174.25	$174.20
Purchase #5	$133.98	4.402%	$139.8778	$139.88	$139.90	$139.90
Purchase #6	$70.37	9.163%	$76.818	$76.82	$76.80	$76.80
Purchase #7	$66.82	4.384%	$69.7494	$69.75	$69.75	$69.70
7 purchase totals =	$751.87		$798.7941	$798.80	$798.80	$798.70