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	$36.47	10.645%	$40.3522	$40.35	$40.35	$40.40
Purchase #2	$181.49	12.126%	$203.4975	$203.50	$203.50	$203.50
Purchase #3	$209.58	10.267%	$231.0976	$231.10	$231.10	$231.10
Purchase #4	$247.77	3.108%	$255.4707	$255.47	$255.45	$255.50
Purchase #5	$170.48	10.133%	$187.7547	$187.75	$187.75	$187.80
Purchase #6	$75.77	12.612%	$85.3261	$85.33	$85.35	$85.30
Purchase #7	$75.29	3.331%	$77.7979	$77.80	$77.80	$77.80
7 purchase totals =	$996.85		$1,081.2967	$1,081.30	$1,081.30	$1,081.40