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	$210.78	6.762%	$225.0329	$225.03	$225.05	$225.00
Purchase #2	$195.77	5.435%	$206.4101	$206.41	$206.40	$206.40
Purchase #3	$19.50	12.289%	$21.8964	$21.90	$21.90	$21.90
Purchase #4	$71.67	12.258%	$80.4553	$80.46	$80.45	$80.50
Purchase #5	$221.82	11.636%	$247.631	$247.63	$247.65	$247.60
Purchase #6	$89.37	11.793%	$99.9094	$99.91	$99.90	$99.90
Purchase #7	$93.29	5.648%	$98.559	$98.56	$98.55	$98.60
7 purchase totals =	$902.20		$979.8941	$979.90	$979.90	$979.90