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	$24.30	4.527%	$25.4001	$25.40	$25.40	$25.40
Purchase #2	$152.25	4.869%	$159.6631	$159.66	$159.65	$159.70
Purchase #3	$168.83	13.248%	$191.1966	$191.20	$191.20	$191.20
Purchase #4	$121.70	4.661%	$127.3724	$127.37	$127.35	$127.40
Purchase #5	$226.51	11.224%	$251.9335	$251.93	$251.95	$251.90
Purchase #6	$34.90	12.398%	$39.2269	$39.23	$39.25	$39.20
Purchase #7	$102.82	6.850%	$109.8632	$109.86	$109.85	$109.90
7 purchase totals =	$831.31		$904.6558	$904.65	$904.65	$904.70