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	$20.32	5.498%	$21.4372	$21.44	$21.45	$21.40
Purchase #2	$35.89	13.233%	$40.6393	$40.64	$40.65	$40.60
Purchase #3	$70.40	5.564%	$74.3171	$74.32	$74.30	$74.30
Purchase #4	$129.93	7.469%	$139.6345	$139.63	$139.65	$139.60
Purchase #5	$55.72	3.779%	$57.8257	$57.83	$57.85	$57.80
Purchase #6	$65.83	9.213%	$71.8949	$71.89	$71.90	$71.90
Purchase #7	$76.84	10.771%	$85.1164	$85.12	$85.10	$85.10
7 purchase totals =	$454.93		$490.8651	$490.87	$490.90	$490.70