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	$66.75	7.656%	$71.8604	$71.86	$71.85	$71.90
Purchase #2	$61.40	11.222%	$68.2903	$68.29	$68.30	$68.30
Purchase #3	$144.98	9.555%	$158.8328	$158.83	$158.85	$158.80
Purchase #4	$203.64	6.316%	$216.5019	$216.50	$216.50	$216.50
Purchase #5	$93.39	11.322%	$103.9636	$103.96	$103.95	$104.00
Purchase #6	$144.89	7.783%	$156.1668	$156.17	$156.15	$156.20
Purchase #7	$7.64	13.421%	$8.6654	$8.67	$8.65	$8.70
7 purchase totals =	$722.69		$784.2812	$784.28	$784.25	$784.40