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	$180.84	6.800%	$193.1371	$193.14	$193.15	$193.10
Purchase #2	$90.74	13.566%	$103.0498	$103.05	$103.05	$103.00
Purchase #3	$100.81	8.411%	$109.2891	$109.29	$109.30	$109.30
Purchase #4	$9.53	13.825%	$10.8475	$10.85	$10.85	$10.80
Purchase #5	$27.58	12.576%	$31.0485	$31.05	$31.05	$31.00
Purchase #6	$217.33	3.360%	$224.6323	$224.63	$224.65	$224.60
Purchase #7	$148.95	9.104%	$162.5104	$162.51	$162.50	$162.50
7 purchase totals =	$775.78		$834.5147	$834.52	$834.55	$834.30