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	$37.65	11.708%	$42.0581	$42.06	$42.05	$42.10
Purchase #2	$187.71	9.809%	$206.1225	$206.12	$206.10	$206.10
Purchase #3	$204.62	8.437%	$221.8838	$221.88	$221.90	$221.90
Purchase #4	$111.42	11.190%	$123.8879	$123.89	$123.90	$123.90
Purchase #5	$147.52	3.656%	$152.9133	$152.91	$152.90	$152.90
Purchase #6	$209.78	12.859%	$236.7556	$236.76	$236.75	$236.80
Purchase #7	$23.29	8.581%	$25.2885	$25.29	$25.30	$25.30
7 purchase totals =	$921.99		$1,008.9097	$1,008.91	$1,008.90	$1,009.00