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	$82.25	8.609%	$89.3309	$89.33	$89.35	$89.30
Purchase #2	$102.30	6.276%	$108.7203	$108.72	$108.70	$108.70
Purchase #3	$229.89	5.383%	$242.265	$242.27	$242.25	$242.30
Purchase #4	$182.46	4.686%	$191.0101	$191.01	$191.00	$191.00
Purchase #5	$148.65	5.689%	$157.1067	$157.11	$157.10	$157.10
Purchase #6	$17.76	13.425%	$20.1443	$20.14	$20.15	$20.10
Purchase #7	$99.94	4.824%	$104.7611	$104.76	$104.75	$104.80
7 purchase totals =	$863.25		$913.3384	$913.34	$913.30	$913.30