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	$221.76	3.616%	$229.7788	$229.78	$229.80	$229.80
Purchase #2	$42.67	6.234%	$45.33	$45.33	$45.35	$45.30
Purchase #3	$11.57	8.823%	$12.5908	$12.59	$12.60	$12.60
Purchase #4	$194.73	9.653%	$213.5273	$213.53	$213.55	$213.50
Purchase #5	$144.72	11.248%	$160.9981	$161.00	$161.00	$161.00
Purchase #6	$173.85	12.673%	$195.882	$195.88	$195.90	$195.90
Purchase #7	$146.86	9.372%	$160.6237	$160.62	$160.60	$160.60
7 purchase totals =	$936.16		$1,018.7307	$1,018.73	$1,018.80	$1,018.70