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	$22.25	8.150%	$24.0634	$24.06	$24.05	$24.10
Purchase #2	$157.55	4.403%	$164.4869	$164.49	$164.50	$164.50
Purchase #3	$131.71	9.765%	$144.5715	$144.57	$144.55	$144.60
Purchase #4	$101.56	8.108%	$109.7945	$109.79	$109.80	$109.80
Purchase #5	$88.91	12.501%	$100.0246	$100.02	$100.00	$100.00
Purchase #6	$39.52	10.217%	$43.5578	$43.56	$43.55	$43.60
Purchase #7	$147.91	11.302%	$164.6268	$164.63	$164.65	$164.60
7 purchase totals =	$689.41		$751.1255	$751.12	$751.10	$751.20