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	$150.48	12.490%	$169.275	$169.28	$169.30	$169.30
Purchase #2	$109.41	9.570%	$119.8805	$119.88	$119.90	$119.90
Purchase #3	$37.89	7.610%	$40.7734	$40.77	$40.75	$40.80
Purchase #4	$136.80	5.835%	$144.7823	$144.78	$144.80	$144.80
Purchase #5	$224.66	9.573%	$246.1667	$246.17	$246.15	$246.20
Purchase #6	$47.25	11.107%	$52.4981	$52.50	$52.50	$52.50
Purchase #7	$158.78	3.817%	$164.8406	$164.84	$164.85	$164.80
7 purchase totals =	$865.27		$938.2166	$938.22	$938.25	$938.30