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	$202.64	13.164%	$229.3155	$229.32	$229.30	$229.30
Purchase #2	$122.34	6.162%	$129.8786	$129.88	$129.90	$129.90
Purchase #3	$90.49	4.366%	$94.4408	$94.44	$94.45	$94.40
Purchase #4	$40.81	7.533%	$43.8842	$43.88	$43.90	$43.90
Purchase #5	$178.73	7.238%	$191.6665	$191.67	$191.65	$191.70
Purchase #6	$95.49	7.345%	$102.5037	$102.50	$102.50	$102.50
Purchase #7	$127.55	12.538%	$143.5422	$143.54	$143.55	$143.50
7 purchase totals =	$858.05		$935.2315	$935.23	$935.25	$935.20