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	$41.77	5.119%	$43.9082	$43.91	$43.90	$43.90
Purchase #2	$250.78	12.663%	$282.5363	$282.54	$282.55	$282.50
Purchase #3	$116.54	13.470%	$132.2379	$132.24	$132.25	$132.20
Purchase #4	$165.93	9.634%	$181.9157	$181.92	$181.90	$181.90
Purchase #5	$121.89	6.216%	$129.4667	$129.47	$129.45	$129.50
Purchase #6	$102.71	6.628%	$109.5176	$109.52	$109.50	$109.50
Purchase #7	$39.88	10.220%	$43.9557	$43.96	$43.95	$44.00
7 purchase totals =	$839.50		$923.5381	$923.56	$923.50	$923.50