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	$181.79	6.432%	$193.4827	$193.48	$193.50	$193.50
Purchase #2	$125.83	11.443%	$140.2287	$140.23	$140.25	$140.20
Purchase #3	$95.80	3.178%	$98.8445	$98.84	$98.85	$98.80
Purchase #4	$112.30	10.284%	$123.8489	$123.85	$123.85	$123.80
Purchase #5	$85.43	10.401%	$94.3156	$94.32	$94.30	$94.30
Purchase #6	$19.71	10.842%	$21.847	$21.85	$21.85	$21.80
Purchase #7	$35.44	10.400%	$39.1258	$39.13	$39.15	$39.10
7 purchase totals =	$656.30		$711.6932	$711.70	$711.75	$711.50