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	$94.93	5.346%	$100.005	$100.01	$100.00	$100.00
Purchase #2	$165.56	7.148%	$177.3942	$177.39	$177.40	$177.40
Purchase #3	$70.56	10.558%	$78.0097	$78.01	$78.00	$78.00
Purchase #4	$180.51	8.655%	$196.1331	$196.13	$196.15	$196.10
Purchase #5	$142.49	12.510%	$160.3155	$160.32	$160.30	$160.30
Purchase #6	$27.77	10.416%	$30.6625	$30.66	$30.65	$30.70
Purchase #7	$141.48	8.760%	$153.8736	$153.87	$153.85	$153.90
7 purchase totals =	$823.30		$896.3936	$896.39	$896.35	$896.40