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	$109.59	5.142%	$115.2251	$115.23	$115.25	$115.20
Purchase #2	$67.47	10.849%	$74.7898	$74.79	$74.80	$74.80
Purchase #3	$181.89	5.498%	$191.8903	$191.89	$191.90	$191.90
Purchase #4	$135.78	4.856%	$142.3735	$142.37	$142.35	$142.40
Purchase #5	$100.92	8.859%	$109.8605	$109.86	$109.85	$109.90
Purchase #6	$107.41	13.499%	$121.9093	$121.91	$121.90	$121.90
Purchase #7	$104.51	11.129%	$116.1409	$116.14	$116.15	$116.10
7 purchase totals =	$807.57		$872.1894	$872.19	$872.20	$872.20