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	$138.50	10.311%	$152.7807	$152.78	$152.80	$152.80
Purchase #2	$223.67	11.446%	$249.2713	$249.27	$249.25	$249.30
Purchase #3	$66.81	9.374%	$73.0728	$73.07	$73.05	$73.10
Purchase #4	$85.79	4.787%	$89.8968	$89.90	$89.90	$89.90
Purchase #5	$114.55	11.678%	$127.9271	$127.93	$127.95	$127.90
Purchase #6	$82.87	10.292%	$91.399	$91.40	$91.40	$91.40
Purchase #7	$6.75	10.246%	$7.4416	$7.44	$7.45	$7.40
7 purchase totals =	$718.94		$791.7893	$791.79	$791.80	$791.80