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	$85.48	6.405%	$90.955	$90.96	$90.95	$91.00
Purchase #2	$230.84	5.774%	$244.1687	$244.17	$244.15	$244.20
Purchase #3	$218.54	5.851%	$231.3268	$231.33	$231.35	$231.30
Purchase #4	$148.70	10.640%	$164.5217	$164.52	$164.50	$164.50
Purchase #5	$121.89	11.722%	$136.1779	$136.18	$136.20	$136.20
Purchase #6	$185.58	7.151%	$198.8508	$198.85	$198.85	$198.90
Purchase #7	$72.71	5.139%	$76.4466	$76.45	$76.45	$76.40
7 purchase totals =	$1,063.74		$1,142.4475	$1,142.46	$1,142.45	$1,142.50