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	$108.90	6.181%	$115.6311	$115.63	$115.65	$115.60
Purchase #2	$77.33	10.139%	$85.1705	$85.17	$85.15	$85.20
Purchase #3	$151.40	9.792%	$166.2251	$166.23	$166.25	$166.20
Purchase #4	$47.74	3.207%	$49.271	$49.27	$49.25	$49.30
Purchase #5	$170.57	8.739%	$185.4761	$185.48	$185.50	$185.50
Purchase #6	$189.78	3.712%	$196.8246	$196.82	$196.80	$196.80
Purchase #7	$27.59	11.785%	$30.8415	$30.84	$30.85	$30.80
7 purchase totals =	$773.31		$829.4399	$829.44	$829.45	$829.40