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	$195.48	9.123%	$213.3136	$213.31	$213.30	$213.30
Purchase #2	$226.74	7.851%	$244.5414	$244.54	$244.55	$244.50
Purchase #3	$139.33	6.197%	$147.9643	$147.96	$147.95	$148.00
Purchase #4	$131.90	9.394%	$144.2907	$144.29	$144.30	$144.30
Purchase #5	$9.89	11.494%	$11.0268	$11.03	$11.05	$11.00
Purchase #6	$17.39	8.502%	$18.8685	$18.87	$18.85	$18.90
Purchase #7	$212.72	4.806%	$222.9433	$222.94	$222.95	$222.90
7 purchase totals =	$933.45		$1,002.9486	$1,002.94	$1,002.95	$1,002.90