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	$79.62	4.109%	$82.8916	$82.89	$82.90	$82.90
Purchase #2	$215.34	11.248%	$239.5614	$239.56	$239.55	$239.60
Purchase #3	$147.38	13.387%	$167.1098	$167.11	$167.10	$167.10
Purchase #4	$62.77	4.806%	$65.7867	$65.79	$65.80	$65.80
Purchase #5	$137.47	7.858%	$148.2724	$148.27	$148.25	$148.30
Purchase #6	$71.79	11.165%	$79.8054	$79.81	$79.80	$79.80
Purchase #7	$37.83	4.552%	$39.552	$39.55	$39.55	$39.60
7 purchase totals =	$752.20		$822.9793	$822.98	$822.95	$823.10