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	$94.37	4.139%	$98.276	$98.28	$98.30	$98.30
Purchase #2	$132.69	6.155%	$140.8571	$140.86	$140.85	$140.90
Purchase #3	$23.77	10.455%	$26.2552	$26.26	$26.25	$26.30
Purchase #4	$46.39	4.150%	$48.3152	$48.32	$48.30	$48.30
Purchase #5	$113.81	13.152%	$128.7783	$128.78	$128.80	$128.80
Purchase #6	$142.59	7.283%	$152.9748	$152.97	$152.95	$153.00
Purchase #7	$71.47	9.223%	$78.0617	$78.06	$78.05	$78.10
7 purchase totals =	$625.09		$673.5183	$673.53	$673.50	$673.70