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	$129.87	8.765%	$141.2531	$141.25	$141.25	$141.30
Purchase #2	$218.96	4.277%	$228.3249	$228.32	$228.30	$228.30
Purchase #3	$90.75	9.650%	$99.5074	$99.51	$99.50	$99.50
Purchase #4	$139.62	7.677%	$150.3386	$150.34	$150.35	$150.30
Purchase #5	$74.25	4.570%	$77.6432	$77.64	$77.65	$77.60
Purchase #6	$219.92	12.398%	$247.1857	$247.19	$247.20	$247.20
Purchase #7	$63.78	13.148%	$72.1658	$72.17	$72.15	$72.20
7 purchase totals =	$937.15		$1,016.4187	$1,016.42	$1,016.40	$1,016.40