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	$166.59	3.448%	$172.334	$172.33	$172.35	$172.30
Purchase #2	$115.73	11.280%	$128.7843	$128.78	$128.80	$128.80
Purchase #3	$87.58	5.564%	$92.453	$92.45	$92.45	$92.50
Purchase #4	$67.96	12.276%	$76.3028	$76.30	$76.30	$76.30
Purchase #5	$213.91	4.300%	$223.1081	$223.11	$223.10	$223.10
Purchase #6	$168.80	5.793%	$178.5786	$178.58	$178.60	$178.60
Purchase #7	$100.58	5.555%	$106.1672	$106.17	$106.15	$106.20
7 purchase totals =	$921.15		$977.7280	$977.72	$977.75	$977.80