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	$212.44	12.421%	$238.8272	$238.83	$238.85	$238.80
Purchase #2	$115.67	10.859%	$128.2306	$128.23	$128.25	$128.20
Purchase #3	$105.30	12.320%	$118.273	$118.27	$118.25	$118.30
Purchase #4	$55.83	7.400%	$59.9614	$59.96	$59.95	$60.00
Purchase #5	$188.83	8.123%	$204.1687	$204.17	$204.15	$204.20
Purchase #6	$117.47	3.150%	$121.1703	$121.17	$121.15	$121.20
Purchase #7	$21.41	4.218%	$22.3131	$22.31	$22.30	$22.30
7 purchase totals =	$816.95		$892.9443	$892.94	$892.90	$893.00