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	$236.87	13.297%	$268.3666	$268.37	$268.35	$268.40
Purchase #2	$58.43	9.192%	$63.8009	$63.80	$63.80	$63.80
Purchase #3	$151.41	11.460%	$168.7616	$168.76	$168.75	$168.80
Purchase #4	$127.84	7.796%	$137.8064	$137.81	$137.80	$137.80
Purchase #5	$33.82	11.810%	$37.8141	$37.81	$37.80	$37.80
Purchase #6	$83.47	13.573%	$94.7994	$94.80	$94.80	$94.80
Purchase #7	$96.77	3.108%	$99.7776	$99.78	$99.80	$99.80
7 purchase totals =	$788.61		$871.1266	$871.13	$871.10	$871.20