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	$55.84	5.283%	$58.79	$58.79	$58.80	$58.80
Purchase #2	$85.59	10.743%	$94.7849	$94.78	$94.80	$94.80
Purchase #3	$92.27	7.850%	$99.5132	$99.51	$99.50	$99.50
Purchase #4	$112.89	13.675%	$128.3277	$128.33	$128.35	$128.30
Purchase #5	$130.61	12.664%	$147.1505	$147.15	$147.15	$147.20
Purchase #6	$215.35	5.797%	$227.8338	$227.83	$227.85	$227.80
Purchase #7	$56.32	7.560%	$60.5778	$60.58	$60.60	$60.60
7 purchase totals =	$748.87		$816.9779	$816.97	$817.05	$817.00