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	$55.77	6.873%	$59.6031	$59.60	$59.60	$59.60
Purchase #2	$141.42	5.373%	$149.0185	$149.02	$149.00	$149.00
Purchase #3	$73.25	5.470%	$77.2568	$77.26	$77.25	$77.30
Purchase #4	$81.36	10.484%	$89.8898	$89.89	$89.90	$89.90
Purchase #5	$25.76	7.170%	$27.607	$27.61	$27.60	$27.60
Purchase #6	$164.88	9.575%	$180.6673	$180.67	$180.65	$180.70
Purchase #7	$198.59	12.699%	$223.8089	$223.81	$223.80	$223.80
7 purchase totals =	$741.03		$807.8514	$807.86	$807.80	$807.90