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	$51.51	7.593%	$55.4212	$55.42	$55.40	$55.40
Purchase #2	$135.27	11.540%	$150.8802	$150.88	$150.90	$150.90
Purchase #3	$184.32	13.672%	$209.5202	$209.52	$209.50	$209.50
Purchase #4	$216.64	5.365%	$228.2627	$228.26	$228.25	$228.30
Purchase #5	$220.46	10.408%	$243.4055	$243.41	$243.40	$243.40
Purchase #6	$109.32	3.354%	$112.9866	$112.99	$113.00	$113.00
Purchase #7	$154.76	11.802%	$173.0248	$173.02	$173.00	$173.00
7 purchase totals =	$1,072.28		$1,173.5012	$1,173.50	$1,173.45	$1,173.50