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	$75.46	13.711%	$85.8063	$85.81	$85.80	$85.80
Purchase #2	$248.47	10.103%	$273.5729	$273.57	$273.55	$273.60
Purchase #3	$84.81	6.139%	$90.0165	$90.02	$90.00	$90.00
Purchase #4	$134.65	5.459%	$142.0005	$142.00	$142.00	$142.00
Purchase #5	$113.72	9.434%	$124.4483	$124.45	$124.45	$124.40
Purchase #6	$25.38	10.731%	$28.1035	$28.10	$28.10	$28.10
Purchase #7	$105.33	7.393%	$113.117	$113.12	$113.10	$113.10
7 purchase totals =	$787.82		$857.0650	$857.07	$857.00	$857.00