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	$41.82	9.808%	$45.9217	$45.92	$45.90	$45.90
Purchase #2	$109.98	6.586%	$117.2233	$117.22	$117.20	$117.20
Purchase #3	$243.28	11.267%	$270.6904	$270.69	$270.70	$270.70
Purchase #4	$129.36	11.836%	$144.671	$144.67	$144.65	$144.70
Purchase #5	$46.31	3.451%	$47.9082	$47.91	$47.90	$47.90
Purchase #6	$31.56	10.562%	$34.8934	$34.89	$34.90	$34.90
Purchase #7	$42.32	3.777%	$43.9184	$43.92	$43.90	$43.90
7 purchase totals =	$644.63		$705.2264	$705.22	$705.15	$705.20