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	$35.37	10.846%	$39.2062	$39.21	$39.20	$39.20
Purchase #2	$13.53	9.364%	$14.7969	$14.80	$14.80	$14.80
Purchase #3	$42.84	8.445%	$46.4578	$46.46	$46.45	$46.50
Purchase #4	$50.27	9.521%	$55.0562	$55.06	$55.05	$55.10
Purchase #5	$235.67	3.477%	$243.8642	$243.86	$243.85	$243.90
Purchase #6	$79.55	12.480%	$89.4778	$89.48	$89.50	$89.50
Purchase #7	$64.40	7.769%	$69.4032	$69.40	$69.40	$69.40
7 purchase totals =	$521.63		$558.2623	$558.27	$558.25	$558.40