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	$86.58	4.802%	$90.7376	$90.74	$90.75	$90.70
Purchase #2	$250.42	12.617%	$282.0155	$282.02	$282.00	$282.00
Purchase #3	$42.52	13.159%	$48.1152	$48.12	$48.10	$48.10
Purchase #4	$171.45	8.499%	$186.0215	$186.02	$186.00	$186.00
Purchase #5	$139.93	12.171%	$156.9609	$156.96	$156.95	$157.00
Purchase #6	$65.76	7.686%	$70.8143	$70.81	$70.80	$70.80
Purchase #7	$49.75	12.278%	$55.8583	$55.86	$55.85	$55.90
7 purchase totals =	$806.41		$890.5233	$890.53	$890.45	$890.50