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	$142.31	6.363%	$151.3652	$151.37	$151.35	$151.40
Purchase #2	$73.73	6.684%	$78.6581	$78.66	$78.65	$78.70
Purchase #3	$33.25	8.192%	$35.9738	$35.97	$35.95	$36.00
Purchase #4	$221.27	3.271%	$228.5077	$228.51	$228.50	$228.50
Purchase #5	$64.53	12.855%	$72.8253	$72.83	$72.85	$72.80
Purchase #6	$235.67	6.227%	$250.3452	$250.35	$250.35	$250.30
Purchase #7	$102.45	10.400%	$113.1048	$113.10	$113.10	$113.10
7 purchase totals =	$873.21		$930.7801	$930.79	$930.75	$930.80