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	$125.70	11.284%	$139.884	$139.88	$139.90	$139.90
Purchase #2	$18.59	12.608%	$20.9338	$20.93	$20.95	$20.90
Purchase #3	$159.65	9.279%	$174.4639	$174.46	$174.45	$174.50
Purchase #4	$82.41	10.705%	$91.232	$91.23	$91.25	$91.20
Purchase #5	$55.69	10.318%	$61.4361	$61.44	$61.45	$61.40
Purchase #6	$18.29	12.337%	$20.5464	$20.55	$20.55	$20.50
Purchase #7	$218.27	4.114%	$227.2496	$227.25	$227.25	$227.20
7 purchase totals =	$678.60		$735.7458	$735.74	$735.80	$735.60