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	$174.33	8.730%	$189.549	$189.55	$189.55	$189.50
Purchase #2	$125.79	10.394%	$138.8646	$138.86	$138.85	$138.90
Purchase #3	$122.92	12.223%	$137.9445	$137.94	$137.95	$137.90
Purchase #4	$128.86	7.636%	$138.6997	$138.70	$138.70	$138.70
Purchase #5	$53.61	10.715%	$59.3543	$59.35	$59.35	$59.40
Purchase #6	$78.83	13.547%	$89.5091	$89.51	$89.50	$89.50
Purchase #7	$93.99	3.142%	$96.9432	$96.94	$96.95	$96.90
7 purchase totals =	$778.33		$850.8644	$850.85	$850.85	$850.80