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	$18.64	12.199%	$20.9139	$20.91	$20.90	$20.90
Purchase #2	$19.33	10.705%	$21.3993	$21.40	$21.40	$21.40
Purchase #3	$105.32	7.736%	$113.4676	$113.47	$113.45	$113.50
Purchase #4	$14.44	3.290%	$14.9151	$14.92	$14.90	$14.90
Purchase #5	$221.31	13.828%	$251.9127	$251.91	$251.90	$251.90
Purchase #6	$37.63	10.220%	$41.4758	$41.48	$41.50	$41.50
Purchase #7	$234.55	11.794%	$262.2128	$262.21	$262.20	$262.20
7 purchase totals =	$651.22		$726.2972	$726.30	$726.25	$726.30