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	$117.51	13.639%	$133.5372	$133.54	$133.55	$133.50
Purchase #2	$49.52	7.279%	$53.1246	$53.12	$53.10	$53.10
Purchase #3	$234.37	11.258%	$260.7554	$260.76	$260.75	$260.80
Purchase #4	$188.91	6.196%	$200.6149	$200.61	$200.60	$200.60
Purchase #5	$6.42	12.444%	$7.2189	$7.22	$7.20	$7.20
Purchase #6	$242.83	6.297%	$258.121	$258.12	$258.10	$258.10
Purchase #7	$43.59	4.615%	$45.6017	$45.60	$45.60	$45.60
7 purchase totals =	$883.15		$958.9737	$958.97	$958.90	$958.90