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	$115.46	4.699%	$120.8855	$120.89	$120.90	$120.90
Purchase #2	$59.55	11.746%	$66.5447	$66.54	$66.55	$66.50
Purchase #3	$131.70	3.780%	$136.6783	$136.68	$136.70	$136.70
Purchase #4	$79.54	8.500%	$86.3009	$86.30	$86.30	$86.30
Purchase #5	$61.79	13.642%	$70.2194	$70.22	$70.20	$70.20
Purchase #6	$108.73	6.587%	$115.892	$115.89	$115.90	$115.90
Purchase #7	$210.30	6.196%	$223.3302	$223.33	$223.35	$223.30
7 purchase totals =	$767.07		$819.8510	$819.85	$819.90	$819.80