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	$80.69	13.426%	$91.5234	$91.52	$91.50	$91.50
Purchase #2	$39.83	7.696%	$42.8953	$42.90	$42.90	$42.90
Purchase #3	$250.25	10.310%	$276.0508	$276.05	$276.05	$276.10
Purchase #4	$33.28	5.449%	$35.0934	$35.09	$35.10	$35.10
Purchase #5	$106.37	4.543%	$111.2024	$111.20	$111.20	$111.20
Purchase #6	$172.54	11.692%	$192.7134	$192.71	$192.70	$192.70
Purchase #7	$69.91	11.222%	$77.7553	$77.76	$77.75	$77.80
7 purchase totals =	$752.87		$827.2340	$827.23	$827.20	$827.30