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	$205.59	12.488%	$231.2641	$231.26	$231.25	$231.30
Purchase #2	$38.77	3.783%	$40.2367	$40.24	$40.25	$40.20
Purchase #3	$91.51	8.774%	$99.5391	$99.54	$99.55	$99.50
Purchase #4	$75.52	10.806%	$83.6807	$83.68	$83.70	$83.70
Purchase #5	$56.45	6.125%	$59.9076	$59.91	$59.90	$59.90
Purchase #6	$232.95	13.461%	$264.3074	$264.31	$264.30	$264.30
Purchase #7	$90.70	5.745%	$95.9107	$95.91	$95.90	$95.90
7 purchase totals =	$791.49		$874.8463	$874.85	$874.85	$874.80