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	$134.56	11.515%	$150.0546	$150.05	$150.05	$150.10
Purchase #2	$100.54	4.764%	$105.3297	$105.33	$105.35	$105.30
Purchase #3	$81.88	13.594%	$93.0108	$93.01	$93.00	$93.00
Purchase #4	$167.51	10.747%	$185.5123	$185.51	$185.50	$185.50
Purchase #5	$57.58	13.354%	$65.2692	$65.27	$65.25	$65.30
Purchase #6	$175.55	3.655%	$181.9664	$181.97	$181.95	$182.00
Purchase #7	$61.33	12.519%	$69.0079	$69.01	$69.00	$69.00
7 purchase totals =	$778.95		$850.1509	$850.15	$850.10	$850.20