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	$27.31	3.709%	$28.3229	$28.32	$28.30	$28.30
Purchase #2	$125.67	4.158%	$130.8954	$130.90	$130.90	$130.90
Purchase #3	$76.30	6.382%	$81.1695	$81.17	$81.15	$81.20
Purchase #4	$179.72	12.106%	$201.4769	$201.48	$201.50	$201.50
Purchase #5	$135.69	11.624%	$151.4626	$151.46	$151.45	$151.50
Purchase #6	$95.93	5.132%	$100.8531	$100.85	$100.85	$100.90
Purchase #7	$54.37	8.689%	$59.0942	$59.09	$59.10	$59.10
7 purchase totals =	$694.99		$753.2746	$753.27	$753.25	$753.40