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	$83.41	4.522%	$87.1818	$87.18	$87.20	$87.20
Purchase #2	$104.80	8.691%	$113.9082	$113.91	$113.90	$113.90
Purchase #3	$179.89	6.415%	$191.4299	$191.43	$191.45	$191.40
Purchase #4	$72.81	8.360%	$78.8969	$78.90	$78.90	$78.90
Purchase #5	$73.92	5.282%	$77.8245	$77.82	$77.80	$77.80
Purchase #6	$78.54	13.658%	$89.267	$89.27	$89.25	$89.30
Purchase #7	$22.84	6.719%	$24.3746	$24.37	$24.35	$24.40
7 purchase totals =	$616.21		$662.8829	$662.88	$662.85	$662.90