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	$120.59	8.701%	$131.0825	$131.08	$131.10	$131.10
Purchase #2	$204.32	6.618%	$217.8419	$217.84	$217.85	$217.80
Purchase #3	$142.78	5.581%	$150.7486	$150.75	$150.75	$150.70
Purchase #4	$63.41	12.410%	$71.2792	$71.28	$71.30	$71.30
Purchase #5	$235.73	3.299%	$243.5067	$243.51	$243.50	$243.50
Purchase #6	$215.90	8.873%	$235.0568	$235.06	$235.05	$235.10
Purchase #7	$51.49	4.197%	$53.651	$53.65	$53.65	$53.70
7 purchase totals =	$1,034.22		$1,103.1667	$1,103.17	$1,103.20	$1,103.20