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	$40.40	4.206%	$42.0992	$42.10	$42.10	$42.10
Purchase #2	$126.90	11.384%	$141.3463	$141.35	$141.35	$141.30
Purchase #3	$96.70	3.839%	$100.4123	$100.41	$100.40	$100.40
Purchase #4	$234.30	3.825%	$243.262	$243.26	$243.25	$243.30
Purchase #5	$202.93	12.850%	$229.0065	$229.01	$229.00	$229.00
Purchase #6	$32.91	3.557%	$34.0806	$34.08	$34.10	$34.10
Purchase #7	$141.93	7.241%	$152.2072	$152.21	$152.20	$152.20
7 purchase totals =	$876.07		$942.4141	$942.42	$942.40	$942.40