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	$167.49	13.822%	$190.6405	$190.64	$190.65	$190.60
Purchase #2	$234.33	13.328%	$265.5615	$265.56	$265.55	$265.60
Purchase #3	$231.59	7.872%	$249.8208	$249.82	$249.80	$249.80
Purchase #4	$180.57	4.431%	$188.5711	$188.57	$188.55	$188.60
Purchase #5	$221.83	4.361%	$231.504	$231.50	$231.50	$231.50
Purchase #6	$30.83	9.171%	$33.6574	$33.66	$33.65	$33.70
Purchase #7	$145.81	3.696%	$151.1991	$151.20	$151.20	$151.20
7 purchase totals =	$1,212.45		$1,310.9544	$1,310.95	$1,310.90	$1,311.00