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	$72.90	8.682%	$79.2292	$79.23	$79.25	$79.20
Purchase #2	$46.74	8.153%	$50.5507	$50.55	$50.55	$50.60
Purchase #3	$198.71	12.705%	$223.9561	$223.96	$223.95	$224.00
Purchase #4	$112.82	13.564%	$128.1229	$128.12	$128.10	$128.10
Purchase #5	$65.33	11.114%	$72.5908	$72.59	$72.60	$72.60
Purchase #6	$59.72	8.518%	$64.8069	$64.81	$64.80	$64.80
Purchase #7	$128.93	4.449%	$134.6661	$134.67	$134.65	$134.70
7 purchase totals =	$685.15		$753.9227	$753.93	$753.90	$754.00