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	$146.43	6.818%	$156.4136	$156.41	$156.40	$156.40
Purchase #2	$222.72	11.809%	$249.021	$249.02	$249.00	$249.00
Purchase #3	$129.64	10.170%	$142.8244	$142.82	$142.80	$142.80
Purchase #4	$85.56	7.581%	$92.0463	$92.05	$92.05	$92.00
Purchase #5	$67.31	7.352%	$72.2586	$72.26	$72.25	$72.30
Purchase #6	$159.36	8.378%	$172.7112	$172.71	$172.70	$172.70
Purchase #7	$131.88	5.145%	$138.6652	$138.67	$138.65	$138.70
7 purchase totals =	$942.90		$1,023.9403	$1,023.94	$1,023.85	$1,023.90