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	$203.45	4.353%	$212.3062	$212.31	$212.30	$212.30
Purchase #2	$75.42	9.449%	$82.5464	$82.55	$82.55	$82.50
Purchase #3	$26.78	4.742%	$28.0499	$28.05	$28.05	$28.00
Purchase #4	$138.78	3.332%	$143.4041	$143.40	$143.40	$143.40
Purchase #5	$80.79	3.555%	$83.6621	$83.66	$83.65	$83.70
Purchase #6	$133.87	9.723%	$146.8862	$146.89	$146.90	$146.90
Purchase #7	$89.40	10.249%	$98.5626	$98.56	$98.55	$98.60
7 purchase totals =	$748.49		$795.4175	$795.42	$795.40	$795.40