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	$19.94	6.797%	$21.2953	$21.30	$21.30	$21.30
Purchase #2	$59.57	7.453%	$64.0098	$64.01	$64.00	$64.00
Purchase #3	$32.48	4.170%	$33.8344	$33.83	$33.85	$33.80
Purchase #4	$29.53	7.414%	$31.7194	$31.72	$31.70	$31.70
Purchase #5	$31.85	12.797%	$35.9258	$35.93	$35.95	$35.90
Purchase #6	$176.55	12.208%	$198.1032	$198.10	$198.10	$198.10
Purchase #7	$181.91	3.862%	$188.9354	$188.94	$188.95	$188.90
7 purchase totals =	$531.83		$573.8233	$573.83	$573.85	$573.70