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	$80.67	12.226%	$90.5327	$90.53	$90.55	$90.50
Purchase #2	$86.76	3.169%	$89.5094	$89.51	$89.50	$89.50
Purchase #3	$233.25	13.225%	$264.0973	$264.10	$264.10	$264.10
Purchase #4	$208.65	11.305%	$232.2379	$232.24	$232.25	$232.20
Purchase #5	$153.87	7.540%	$165.4718	$165.47	$165.45	$165.50
Purchase #6	$102.27	7.618%	$110.0609	$110.06	$110.05	$110.10
Purchase #7	$13.93	11.759%	$15.568	$15.57	$15.55	$15.60
7 purchase totals =	$879.40		$967.4780	$967.48	$967.45	$967.50