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	$71.46	12.405%	$80.3246	$80.32	$80.30	$80.30
Purchase #2	$199.88	12.190%	$224.2454	$224.25	$224.25	$224.20
Purchase #3	$110.89	7.733%	$119.4651	$119.47	$119.45	$119.50
Purchase #4	$189.69	10.213%	$209.063	$209.06	$209.05	$209.10
Purchase #5	$184.85	7.385%	$198.5012	$198.50	$198.50	$198.50
Purchase #6	$75.64	13.530%	$85.8741	$85.87	$85.85	$85.90
Purchase #7	$79.65	11.194%	$88.566	$88.57	$88.55	$88.60
7 purchase totals =	$912.06		$1,006.0394	$1,006.04	$1,005.95	$1,006.10