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	$169.57	6.470%	$180.5412	$180.54	$180.55	$180.50
Purchase #2	$150.58	13.417%	$170.7833	$170.78	$170.80	$170.80
Purchase #3	$169.56	13.173%	$191.8961	$191.90	$191.90	$191.90
Purchase #4	$231.42	13.747%	$263.2333	$263.23	$263.25	$263.20
Purchase #5	$156.58	6.503%	$166.7624	$166.76	$166.75	$166.80
Purchase #6	$109.70	4.811%	$114.9777	$114.98	$115.00	$115.00
Purchase #7	$74.81	10.871%	$82.9426	$82.94	$82.95	$82.90
7 purchase totals =	$1,062.22		$1,171.1366	$1,171.13	$1,171.20	$1,171.10