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	$180.34	3.837%	$187.2596	$187.26	$187.25	$187.30
Purchase #2	$76.91	11.139%	$85.477	$85.48	$85.50	$85.50
Purchase #3	$228.85	7.450%	$245.8993	$245.90	$245.90	$245.90
Purchase #4	$42.47	13.144%	$48.0523	$48.05	$48.05	$48.10
Purchase #5	$91.41	12.147%	$102.5136	$102.51	$102.50	$102.50
Purchase #6	$61.31	10.768%	$67.9119	$67.91	$67.90	$67.90
Purchase #7	$245.73	3.690%	$254.7974	$254.80	$254.80	$254.80
7 purchase totals =	$927.02		$991.9111	$991.91	$991.90	$992.00