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	$37.67	6.338%	$40.0575	$40.06	$40.05	$40.10
Purchase #2	$77.44	8.247%	$83.8265	$83.83	$83.85	$83.80
Purchase #3	$128.98	12.199%	$144.7143	$144.71	$144.70	$144.70
Purchase #4	$140.90	6.769%	$150.4375	$150.44	$150.45	$150.40
Purchase #5	$159.69	3.573%	$165.3957	$165.40	$165.40	$165.40
Purchase #6	$63.54	11.811%	$71.0447	$71.04	$71.05	$71.00
Purchase #7	$86.45	5.707%	$91.3837	$91.38	$91.40	$91.40
7 purchase totals =	$694.67		$746.8599	$746.86	$746.90	$746.80