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	$204.67	12.538%	$230.3315	$230.33	$230.35	$230.30
Purchase #2	$108.96	3.275%	$112.5284	$112.53	$112.55	$112.50
Purchase #3	$147.31	8.867%	$160.372	$160.37	$160.35	$160.40
Purchase #4	$11.62	11.663%	$12.9752	$12.98	$13.00	$13.00
Purchase #5	$90.86	9.129%	$99.1546	$99.15	$99.15	$99.20
Purchase #6	$196.59	7.638%	$211.6055	$211.61	$211.60	$211.60
Purchase #7	$250.57	5.681%	$264.8049	$264.80	$264.80	$264.80
7 purchase totals =	$1,010.58		$1,091.7721	$1,091.77	$1,091.80	$1,091.80