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	$37.49	4.570%	$39.2033	$39.20	$39.20	$39.20
Purchase #2	$111.54	10.192%	$122.9082	$122.91	$122.90	$122.90
Purchase #3	$234.76	13.812%	$267.1851	$267.19	$267.20	$267.20
Purchase #4	$159.25	5.722%	$168.3623	$168.36	$168.35	$168.40
Purchase #5	$80.41	3.788%	$83.4559	$83.46	$83.45	$83.50
Purchase #6	$198.55	11.866%	$222.1099	$222.11	$222.10	$222.10
Purchase #7	$167.46	12.579%	$188.5248	$188.52	$188.50	$188.50
7 purchase totals =	$989.46		$1,091.7495	$1,091.75	$1,091.70	$1,091.80