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	$220.98	13.383%	$250.5538	$250.55	$250.55	$250.60
Purchase #2	$157.52	13.159%	$178.2481	$178.25	$178.25	$178.20
Purchase #3	$91.59	3.402%	$94.7059	$94.71	$94.70	$94.70
Purchase #4	$167.39	11.817%	$187.1705	$187.17	$187.15	$187.20
Purchase #5	$206.57	7.620%	$222.3106	$222.31	$222.30	$222.30
Purchase #6	$20.93	9.304%	$22.8773	$22.88	$22.90	$22.90
Purchase #7	$34.38	11.620%	$38.375	$38.38	$38.40	$38.40
7 purchase totals =	$899.36		$994.2412	$994.25	$994.25	$994.30