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	$104.52	5.550%	$110.3209	$110.32	$110.30	$110.30
Purchase #2	$128.82	10.842%	$142.7867	$142.79	$142.80	$142.80
Purchase #3	$38.62	10.205%	$42.5612	$42.56	$42.55	$42.60
Purchase #4	$212.45	4.141%	$221.2476	$221.25	$221.25	$221.20
Purchase #5	$9.69	7.512%	$10.4179	$10.42	$10.40	$10.40
Purchase #6	$212.44	5.388%	$223.8863	$223.89	$223.90	$223.90
Purchase #7	$219.46	12.802%	$247.5553	$247.56	$247.55	$247.60
7 purchase totals =	$926.00		$998.7759	$998.79	$998.75	$998.80