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	$127.71	9.122%	$139.3597	$139.36	$139.35	$139.40
Purchase #2	$61.91	11.393%	$68.9634	$68.96	$68.95	$69.00
Purchase #3	$94.39	13.192%	$106.8419	$106.84	$106.85	$106.80
Purchase #4	$162.83	4.317%	$169.8594	$169.86	$169.85	$169.90
Purchase #5	$28.56	12.375%	$32.0943	$32.09	$32.10	$32.10
Purchase #6	$127.70	11.197%	$141.9986	$142.00	$142.00	$142.00
Purchase #7	$38.38	7.854%	$41.3944	$41.39	$41.40	$41.40
7 purchase totals =	$641.48		$700.5117	$700.50	$700.50	$700.60