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	$39.41	6.737%	$42.0651	$42.07	$42.05	$42.10
Purchase #2	$76.33	3.149%	$78.7336	$78.73	$78.75	$78.70
Purchase #3	$16.90	13.330%	$19.1528	$19.15	$19.15	$19.20
Purchase #4	$159.37	13.141%	$180.3128	$180.31	$180.30	$180.30
Purchase #5	$6.79	8.212%	$7.3476	$7.35	$7.35	$7.30
Purchase #6	$228.60	10.687%	$253.0305	$253.03	$253.05	$253.00
Purchase #7	$240.43	11.811%	$268.8272	$268.83	$268.85	$268.80
7 purchase totals =	$767.83		$849.4696	$849.47	$849.50	$849.40