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	$91.48	8.386%	$99.1515	$99.15	$99.15	$99.20
Purchase #2	$50.86	13.611%	$57.7826	$57.78	$57.80	$57.80
Purchase #3	$152.90	8.437%	$165.8002	$165.80	$165.80	$165.80
Purchase #4	$54.45	11.426%	$60.6715	$60.67	$60.65	$60.70
Purchase #5	$99.94	8.398%	$108.333	$108.33	$108.35	$108.30
Purchase #6	$246.71	13.833%	$280.8374	$280.84	$280.85	$280.80
Purchase #7	$77.87	9.703%	$85.4257	$85.43	$85.45	$85.40
7 purchase totals =	$774.21		$858.0019	$858.00	$858.05	$858.00