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	$190.30	10.122%	$209.5622	$209.56	$209.55	$209.60
Purchase #2	$40.32	6.150%	$42.7997	$42.80	$42.80	$42.80
Purchase #3	$244.61	10.514%	$270.3283	$270.33	$270.35	$270.30
Purchase #4	$219.99	10.168%	$242.3586	$242.36	$242.35	$242.40
Purchase #5	$134.57	6.251%	$142.982	$142.98	$143.00	$143.00
Purchase #6	$171.59	4.628%	$179.5312	$179.53	$179.55	$179.50
Purchase #7	$209.26	6.848%	$223.5901	$223.59	$223.60	$223.60
7 purchase totals =	$1,210.64		$1,311.1521	$1,311.15	$1,311.20	$1,311.20