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	$75.28	4.300%	$78.517	$78.52	$78.50	$78.50
Purchase #2	$164.87	6.171%	$175.0441	$175.04	$175.05	$175.00
Purchase #3	$91.96	5.332%	$96.8633	$96.86	$96.85	$96.90
Purchase #4	$208.95	6.839%	$223.2401	$223.24	$223.25	$223.20
Purchase #5	$96.61	10.608%	$106.8584	$106.86	$106.85	$106.90
Purchase #6	$91.41	9.575%	$100.1625	$100.16	$100.15	$100.20
Purchase #7	$198.83	3.682%	$206.1509	$206.15	$206.15	$206.20
7 purchase totals =	$927.91		$986.8363	$986.83	$986.80	$986.90