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	$45.53	13.274%	$51.5737	$51.57	$51.55	$51.60
Purchase #2	$66.90	13.404%	$75.8673	$75.87	$75.85	$75.90
Purchase #3	$187.33	6.447%	$199.4072	$199.41	$199.40	$199.40
Purchase #4	$41.25	7.452%	$44.324	$44.32	$44.30	$44.30
Purchase #5	$168.31	13.164%	$190.4663	$190.47	$190.45	$190.50
Purchase #6	$37.64	11.637%	$42.0202	$42.02	$42.00	$42.00
Purchase #7	$144.63	7.236%	$155.0954	$155.10	$155.10	$155.10
7 purchase totals =	$691.59		$758.7541	$758.76	$758.65	$758.80