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	$110.86	9.147%	$121.0004	$121.00	$121.00	$121.00
Purchase #2	$83.75	7.594%	$90.11	$90.11	$90.10	$90.10
Purchase #3	$232.96	4.515%	$243.4781	$243.48	$243.50	$243.50
Purchase #4	$63.26	13.467%	$71.7792	$71.78	$71.80	$71.80
Purchase #5	$69.51	13.252%	$78.7215	$78.72	$78.70	$78.70
Purchase #6	$185.46	5.718%	$196.0646	$196.06	$196.05	$196.10
Purchase #7	$129.80	12.255%	$145.707	$145.71	$145.70	$145.70
7 purchase totals =	$875.60		$946.8608	$946.86	$946.85	$946.90