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	$24.27	9.166%	$26.4946	$26.49	$26.50	$26.50
Purchase #2	$143.36	10.658%	$158.6393	$158.64	$158.65	$158.60
Purchase #3	$233.93	6.349%	$248.7822	$248.78	$248.80	$248.80
Purchase #4	$215.27	3.187%	$222.1307	$222.13	$222.15	$222.10
Purchase #5	$238.57	12.143%	$267.5396	$267.54	$267.55	$267.50
Purchase #6	$223.81	9.603%	$245.3025	$245.30	$245.30	$245.30
Purchase #7	$71.27	9.670%	$78.1618	$78.16	$78.15	$78.20
7 purchase totals =	$1,150.48		$1,247.0507	$1,247.04	$1,247.10	$1,247.00