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	$187.62	5.590%	$198.108	$198.11	$198.10	$198.10
Purchase #2	$220.98	8.752%	$240.3202	$240.32	$240.30	$240.30
Purchase #3	$223.96	13.861%	$255.0031	$255.00	$255.00	$255.00
Purchase #4	$53.36	5.388%	$56.235	$56.24	$56.25	$56.20
Purchase #5	$110.88	10.340%	$122.345	$122.35	$122.35	$122.30
Purchase #6	$30.64	9.514%	$33.5551	$33.56	$33.55	$33.60
Purchase #7	$92.91	7.494%	$99.8727	$99.87	$99.85	$99.90
7 purchase totals =	$920.35		$1,005.4391	$1,005.45	$1,005.40	$1,005.40