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	$37.71	6.480%	$40.1536	$40.15	$40.15	$40.20
Purchase #2	$54.92	12.241%	$61.6428	$61.64	$61.65	$61.60
Purchase #3	$57.32	7.456%	$61.5938	$61.59	$61.60	$61.60
Purchase #4	$144.43	11.213%	$160.6249	$160.62	$160.60	$160.60
Purchase #5	$155.49	8.526%	$168.7471	$168.75	$168.75	$168.70
Purchase #6	$97.37	13.217%	$110.2394	$110.24	$110.25	$110.20
Purchase #7	$6.44	7.230%	$6.9056	$6.91	$6.90	$6.90
7 purchase totals =	$553.68		$609.9072	$609.90	$609.90	$609.80