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	$233.56	10.359%	$257.7545	$257.75	$257.75	$257.80
Purchase #2	$141.78	12.768%	$159.8825	$159.88	$159.90	$159.90
Purchase #3	$92.82	11.809%	$103.7811	$103.78	$103.80	$103.80
Purchase #4	$162.87	10.330%	$179.6945	$179.69	$179.70	$179.70
Purchase #5	$211.36	4.115%	$220.0575	$220.06	$220.05	$220.10
Purchase #6	$115.44	9.501%	$126.408	$126.41	$126.40	$126.40
Purchase #7	$13.31	4.391%	$13.8944	$13.89	$13.90	$13.90
7 purchase totals =	$971.14		$1,061.4725	$1,061.46	$1,061.50	$1,061.60