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	$47.86	6.519%	$50.98	$50.98	$51.00	$51.00
Purchase #2	$111.42	5.437%	$117.4779	$117.48	$117.50	$117.50
Purchase #3	$221.80	9.796%	$243.5275	$243.53	$243.55	$243.50
Purchase #4	$164.76	8.375%	$178.5587	$178.56	$178.55	$178.60
Purchase #5	$54.32	9.363%	$59.406	$59.41	$59.40	$59.40
Purchase #6	$234.80	11.234%	$261.1774	$261.18	$261.20	$261.20
Purchase #7	$231.73	10.174%	$255.3062	$255.31	$255.30	$255.30
7 purchase totals =	$1,066.69		$1,166.4337	$1,166.45	$1,166.50	$1,166.50