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	$223.29	13.682%	$253.8405	$253.84	$253.85	$253.80
Purchase #2	$24.78	4.402%	$25.8708	$25.87	$25.85	$25.90
Purchase #3	$240.73	3.842%	$249.9788	$249.98	$250.00	$250.00
Purchase #4	$74.78	11.819%	$83.6182	$83.62	$83.60	$83.60
Purchase #5	$37.97	11.375%	$42.2891	$42.29	$42.30	$42.30
Purchase #6	$19.65	3.816%	$20.3998	$20.40	$20.40	$20.40
Purchase #7	$171.56	5.359%	$180.7539	$180.75	$180.75	$180.80
7 purchase totals =	$792.76		$856.7511	$856.75	$856.75	$856.80