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	$39.48	8.278%	$42.7482	$42.75	$42.75	$42.70
Purchase #2	$129.94	13.811%	$147.886	$147.89	$147.90	$147.90
Purchase #3	$99.63	9.366%	$108.9613	$108.96	$108.95	$109.00
Purchase #4	$31.39	3.215%	$32.3992	$32.40	$32.40	$32.40
Purchase #5	$162.45	10.133%	$178.9111	$178.91	$178.90	$178.90
Purchase #6	$151.77	13.124%	$171.6883	$171.69	$171.70	$171.70
Purchase #7	$145.57	10.112%	$160.29	$160.29	$160.30	$160.30
7 purchase totals =	$760.23		$842.8841	$842.89	$842.90	$842.90