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	$70.98	9.736%	$77.8906	$77.89	$77.90	$77.90
Purchase #2	$240.34	8.391%	$260.5069	$260.51	$260.50	$260.50
Purchase #3	$146.88	6.257%	$156.0703	$156.07	$156.05	$156.10
Purchase #4	$123.91	3.712%	$128.5095	$128.51	$128.50	$128.50
Purchase #5	$240.26	12.645%	$270.6409	$270.64	$270.65	$270.60
Purchase #6	$25.39	13.666%	$28.8598	$28.86	$28.85	$28.90
Purchase #7	$158.97	9.659%	$174.3249	$174.32	$174.30	$174.30
7 purchase totals =	$1,006.73		$1,096.8029	$1,096.80	$1,096.75	$1,096.80