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	$6.73	5.351%	$7.0901	$7.09	$7.10	$7.10
Purchase #2	$153.64	11.642%	$171.5268	$171.53	$171.55	$171.50
Purchase #3	$224.73	6.399%	$239.1105	$239.11	$239.10	$239.10
Purchase #4	$105.34	3.703%	$109.2407	$109.24	$109.25	$109.20
Purchase #5	$104.53	7.614%	$112.4889	$112.49	$112.50	$112.50
Purchase #6	$41.84	6.299%	$44.4755	$44.48	$44.50	$44.50
Purchase #7	$144.59	4.479%	$151.0662	$151.07	$151.05	$151.10
7 purchase totals =	$781.40		$834.9987	$835.01	$835.05	$835.00