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	$93.47	8.483%	$101.3991	$101.40	$101.40	$101.40
Purchase #2	$48.77	12.183%	$54.7116	$54.71	$54.70	$54.70
Purchase #3	$39.48	6.658%	$42.1086	$42.11	$42.10	$42.10
Purchase #4	$249.75	12.255%	$280.3569	$280.36	$280.35	$280.40
Purchase #5	$143.42	4.740%	$150.2181	$150.22	$150.20	$150.20
Purchase #6	$86.77	11.192%	$96.4813	$96.48	$96.50	$96.50
Purchase #7	$122.63	6.645%	$130.7788	$130.78	$130.80	$130.80
7 purchase totals =	$784.29		$856.0544	$856.06	$856.05	$856.10