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	$68.98	13.377%	$78.2075	$78.21	$78.20	$78.20
Purchase #2	$233.53	8.492%	$253.3614	$253.36	$253.35	$253.40
Purchase #3	$153.89	3.604%	$159.4362	$159.44	$159.45	$159.40
Purchase #4	$227.75	12.516%	$256.2552	$256.26	$256.25	$256.30
Purchase #5	$81.72	11.547%	$91.1562	$91.16	$91.15	$91.20
Purchase #6	$48.36	6.231%	$51.3733	$51.37	$51.35	$51.40
Purchase #7	$149.66	12.269%	$168.0218	$168.02	$168.00	$168.00
7 purchase totals =	$963.89		$1,057.8116	$1,057.82	$1,057.75	$1,057.90