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	$220.83	8.370%	$239.3135	$239.31	$239.30	$239.30
Purchase #2	$127.90	9.417%	$139.9443	$139.94	$139.95	$139.90
Purchase #3	$176.28	11.608%	$196.7426	$196.74	$196.75	$196.70
Purchase #4	$157.95	7.563%	$169.8958	$169.90	$169.90	$169.90
Purchase #5	$135.74	5.216%	$142.8202	$142.82	$142.80	$142.80
Purchase #6	$89.77	6.760%	$95.8385	$95.84	$95.85	$95.80
Purchase #7	$104.55	5.535%	$110.3368	$110.34	$110.35	$110.30
7 purchase totals =	$1,013.02		$1,094.8917	$1,094.89	$1,094.90	$1,094.70