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	$82.76	10.616%	$91.5458	$91.55	$91.55	$91.50
Purchase #2	$168.79	5.166%	$177.5097	$177.51	$177.50	$177.50
Purchase #3	$129.28	11.244%	$143.8162	$143.82	$143.80	$143.80
Purchase #4	$85.53	13.801%	$97.334	$97.33	$97.35	$97.30
Purchase #5	$137.96	12.410%	$155.0808	$155.08	$155.10	$155.10
Purchase #6	$89.73	9.410%	$98.1736	$98.17	$98.15	$98.20
Purchase #7	$65.25	9.857%	$71.6817	$71.68	$71.70	$71.70
7 purchase totals =	$759.30		$835.1418	$835.14	$835.15	$835.10