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	$116.37	7.301%	$124.8662	$124.87	$124.85	$124.90
Purchase #2	$73.74	6.595%	$78.6032	$78.60	$78.60	$78.60
Purchase #3	$56.51	4.848%	$59.2496	$59.25	$59.25	$59.20
Purchase #4	$37.33	3.498%	$38.6358	$38.64	$38.65	$38.60
Purchase #5	$67.77	13.800%	$77.1223	$77.12	$77.10	$77.10
Purchase #6	$133.50	13.690%	$151.7762	$151.78	$151.80	$151.80
Purchase #7	$70.35	3.470%	$72.7911	$72.79	$72.80	$72.80
7 purchase totals =	$555.57		$603.0444	$603.05	$603.05	$603.00