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	$238.69	11.373%	$265.8362	$265.84	$265.85	$265.80
Purchase #2	$119.96	6.349%	$127.5763	$127.58	$127.60	$127.60
Purchase #3	$200.57	7.846%	$216.3067	$216.31	$216.30	$216.30
Purchase #4	$246.43	8.696%	$267.8596	$267.86	$267.85	$267.90
Purchase #5	$148.30	10.857%	$164.4009	$164.40	$164.40	$164.40
Purchase #6	$234.40	4.577%	$245.1285	$245.13	$245.15	$245.10
Purchase #7	$191.25	13.347%	$216.7761	$216.78	$216.80	$216.80
7 purchase totals =	$1,379.60		$1,503.8843	$1,503.90	$1,503.95	$1,503.90