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	$27.34	4.302%	$28.5162	$28.52	$28.50	$28.50
Purchase #2	$82.86	8.319%	$89.7531	$89.75	$89.75	$89.80
Purchase #3	$82.87	8.270%	$89.7233	$89.72	$89.70	$89.70
Purchase #4	$156.71	7.207%	$168.0041	$168.00	$168.00	$168.00
Purchase #5	$113.31	9.250%	$123.7912	$123.79	$123.80	$123.80
Purchase #6	$127.58	8.839%	$138.8568	$138.86	$138.85	$138.90
Purchase #7	$243.63	9.390%	$266.5069	$266.51	$266.50	$266.50
7 purchase totals =	$834.30		$905.1516	$905.15	$905.10	$905.20