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	$7.65	11.785%	$8.5516	$8.55	$8.55	$8.60
Purchase #2	$43.71	5.407%	$46.0734	$46.07	$46.05	$46.10
Purchase #3	$250.37	9.592%	$274.3855	$274.39	$274.40	$274.40
Purchase #4	$167.89	11.539%	$187.2628	$187.26	$187.25	$187.30
Purchase #5	$104.27	9.228%	$113.892	$113.89	$113.90	$113.90
Purchase #6	$13.25	3.357%	$13.6948	$13.69	$13.70	$13.70
Purchase #7	$104.61	4.659%	$109.4838	$109.48	$109.50	$109.50
7 purchase totals =	$691.75		$753.3439	$753.33	$753.35	$753.50