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	$33.61	11.428%	$37.451	$37.45	$37.45	$37.50
Purchase #2	$159.94	3.402%	$165.3812	$165.38	$165.40	$165.40
Purchase #3	$189.89	7.129%	$203.4273	$203.43	$203.45	$203.40
Purchase #4	$62.49	5.551%	$65.9588	$65.96	$65.95	$66.00
Purchase #5	$249.98	7.799%	$269.4759	$269.48	$269.50	$269.50
Purchase #6	$86.79	6.417%	$92.3593	$92.36	$92.35	$92.40
Purchase #7	$94.57	9.569%	$103.6194	$103.62	$103.60	$103.60
7 purchase totals =	$877.27		$937.6729	$937.68	$937.70	$937.80