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	$128.38	7.271%	$137.7145	$137.71	$137.70	$137.70
Purchase #2	$141.83	6.400%	$150.9071	$150.91	$150.90	$150.90
Purchase #3	$189.38	11.417%	$211.0015	$211.00	$211.00	$211.00
Purchase #4	$133.60	9.874%	$146.7917	$146.79	$146.80	$146.80
Purchase #5	$140.89	8.199%	$152.4416	$152.44	$152.45	$152.40
Purchase #6	$98.46	6.285%	$104.6482	$104.65	$104.65	$104.60
Purchase #7	$162.69	4.774%	$170.4568	$170.46	$170.45	$170.50
7 purchase totals =	$995.23		$1,073.9614	$1,073.96	$1,073.95	$1,073.90