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	$237.62	6.846%	$253.8875	$253.89	$253.90	$253.90
Purchase #2	$114.37	11.776%	$127.8382	$127.84	$127.85	$127.80
Purchase #3	$80.62	6.265%	$85.6708	$85.67	$85.65	$85.70
Purchase #4	$180.87	11.400%	$201.4892	$201.49	$201.50	$201.50
Purchase #5	$79.83	7.591%	$85.8899	$85.89	$85.90	$85.90
Purchase #6	$45.73	13.381%	$51.8491	$51.85	$51.85	$51.80
Purchase #7	$172.47	8.627%	$187.349	$187.35	$187.35	$187.30
7 purchase totals =	$911.51		$993.9737	$993.98	$994.00	$993.90