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	$79.38	12.830%	$89.5645	$89.56	$89.55	$89.60
Purchase #2	$77.79	6.600%	$82.9241	$82.92	$82.90	$82.90
Purchase #3	$193.55	3.266%	$199.8713	$199.87	$199.85	$199.90
Purchase #4	$50.79	6.102%	$53.8892	$53.89	$53.90	$53.90
Purchase #5	$178.60	6.837%	$190.8109	$190.81	$190.80	$190.80
Purchase #6	$70.42	13.484%	$79.9154	$79.92	$79.90	$79.90
Purchase #7	$219.27	3.807%	$227.6176	$227.62	$227.60	$227.60
7 purchase totals =	$869.80		$924.5930	$924.59	$924.50	$924.60