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	$233.45	13.840%	$265.7595	$265.76	$265.75	$265.80
Purchase #2	$246.75	8.301%	$267.2327	$267.23	$267.25	$267.20
Purchase #3	$36.73	13.107%	$41.5442	$41.54	$41.55	$41.50
Purchase #4	$56.29	5.703%	$59.5002	$59.50	$59.50	$59.50
Purchase #5	$206.63	11.241%	$229.8573	$229.86	$229.85	$229.90
Purchase #6	$45.47	11.169%	$50.5485	$50.55	$50.55	$50.50
Purchase #7	$71.60	8.872%	$77.9524	$77.95	$77.95	$78.00
7 purchase totals =	$896.92		$992.3948	$992.39	$992.40	$992.40