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	$201.93	3.550%	$209.0985	$209.10	$209.10	$209.10
Purchase #2	$52.42	4.716%	$54.8921	$54.89	$54.90	$54.90
Purchase #3	$68.89	5.232%	$72.4943	$72.49	$72.50	$72.50
Purchase #4	$202.27	10.650%	$223.8118	$223.81	$223.80	$223.80
Purchase #5	$75.84	7.367%	$81.4271	$81.43	$81.45	$81.40
Purchase #6	$28.61	4.557%	$29.9138	$29.91	$29.90	$29.90
Purchase #7	$133.84	12.415%	$150.4562	$150.46	$150.45	$150.50
7 purchase totals =	$763.80		$822.0938	$822.09	$822.10	$822.10