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	$90.69	11.563%	$101.1765	$101.18	$101.20	$101.20
Purchase #2	$81.94	8.804%	$89.154	$89.15	$89.15	$89.20
Purchase #3	$193.98	12.146%	$217.5408	$217.54	$217.55	$217.50
Purchase #4	$82.48	9.489%	$90.3065	$90.31	$90.30	$90.30
Purchase #5	$164.79	6.593%	$175.6546	$175.65	$175.65	$175.70
Purchase #6	$171.88	7.242%	$184.3275	$184.33	$184.35	$184.30
Purchase #7	$229.60	5.441%	$242.0925	$242.09	$242.10	$242.10
7 purchase totals =	$1,015.36		$1,100.2524	$1,100.25	$1,100.30	$1,100.30