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	$46.56	9.837%	$51.1401	$51.14	$51.15	$51.10
Purchase #2	$227.78	9.847%	$250.2095	$250.21	$250.20	$250.20
Purchase #3	$71.33	9.170%	$77.871	$77.87	$77.85	$77.90
Purchase #4	$250.82	9.816%	$275.4405	$275.44	$275.45	$275.40
Purchase #5	$165.99	12.547%	$186.8168	$186.82	$186.80	$186.80
Purchase #6	$193.78	10.271%	$213.6831	$213.68	$213.70	$213.70
Purchase #7	$87.56	9.282%	$95.6873	$95.69	$95.70	$95.70
7 purchase totals =	$1,043.82		$1,150.8483	$1,150.85	$1,150.85	$1,150.80