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	$79.59	3.238%	$82.1671	$82.17	$82.15	$82.20
Purchase #2	$145.90	9.562%	$159.851	$159.85	$159.85	$159.90
Purchase #3	$42.93	9.137%	$46.8525	$46.85	$46.85	$46.90
Purchase #4	$50.72	8.680%	$55.1225	$55.12	$55.10	$55.10
Purchase #5	$204.79	9.537%	$224.3208	$224.32	$224.30	$224.30
Purchase #6	$38.36	3.652%	$39.7609	$39.76	$39.75	$39.80
Purchase #7	$205.76	6.558%	$219.2537	$219.25	$219.25	$219.30
7 purchase totals =	$768.05		$827.3285	$827.32	$827.25	$827.50