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	$71.68	13.435%	$81.3102	$81.31	$81.30	$81.30
Purchase #2	$83.74	13.481%	$95.029	$95.03	$95.05	$95.00
Purchase #3	$36.32	12.235%	$40.7638	$40.76	$40.75	$40.80
Purchase #4	$31.45	3.194%	$32.4545	$32.45	$32.45	$32.50
Purchase #5	$245.90	11.148%	$273.3129	$273.31	$273.30	$273.30
Purchase #6	$45.91	5.783%	$48.565	$48.57	$48.55	$48.60
Purchase #7	$198.61	6.660%	$211.8374	$211.84	$211.85	$211.80
7 purchase totals =	$713.61		$783.2728	$783.27	$783.25	$783.30