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	$135.62	5.511%	$143.094	$143.09	$143.10	$143.10
Purchase #2	$63.30	13.460%	$71.8202	$71.82	$71.80	$71.80
Purchase #3	$90.28	13.837%	$102.772	$102.77	$102.75	$102.80
Purchase #4	$106.52	7.860%	$114.8925	$114.89	$114.90	$114.90
Purchase #5	$93.82	7.587%	$100.9381	$100.94	$100.95	$100.90
Purchase #6	$71.74	10.626%	$79.3631	$79.36	$79.35	$79.40
Purchase #7	$220.61	10.166%	$243.0372	$243.04	$243.05	$243.00
7 purchase totals =	$781.89		$855.9171	$855.91	$855.90	$855.90