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	$100.82	9.222%	$110.1176	$110.12	$110.10	$110.10
Purchase #2	$37.89	12.807%	$42.7426	$42.74	$42.75	$42.70
Purchase #3	$159.69	12.689%	$179.9531	$179.95	$179.95	$180.00
Purchase #4	$215.46	10.861%	$238.8611	$238.86	$238.85	$238.90
Purchase #5	$69.31	5.382%	$73.0403	$73.04	$73.05	$73.00
Purchase #6	$119.55	7.162%	$128.1122	$128.11	$128.10	$128.10
Purchase #7	$186.92	9.835%	$205.3036	$205.30	$205.30	$205.30
7 purchase totals =	$889.64		$978.1305	$978.12	$978.10	$978.10