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	$77.88	5.486%	$82.1525	$82.15	$82.15	$82.20
Purchase #2	$158.56	12.803%	$178.8604	$178.86	$178.85	$178.90
Purchase #3	$250.33	7.494%	$269.0897	$269.09	$269.10	$269.10
Purchase #4	$95.86	6.254%	$101.8551	$101.86	$101.85	$101.90
Purchase #5	$163.80	13.145%	$185.3315	$185.33	$185.35	$185.30
Purchase #6	$119.50	7.622%	$128.6083	$128.61	$128.60	$128.60
Purchase #7	$242.53	10.507%	$268.0126	$268.01	$268.00	$268.00
7 purchase totals =	$1,108.46		$1,213.9101	$1,213.91	$1,213.90	$1,214.00