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	$154.36	9.132%	$168.4562	$168.46	$168.45	$168.50
Purchase #2	$69.88	10.423%	$77.1636	$77.16	$77.15	$77.20
Purchase #3	$116.28	6.179%	$123.4649	$123.46	$123.45	$123.50
Purchase #4	$171.35	6.352%	$182.2342	$182.23	$182.25	$182.20
Purchase #5	$223.85	7.560%	$240.7731	$240.77	$240.75	$240.80
Purchase #6	$139.82	3.427%	$144.6116	$144.61	$144.60	$144.60
Purchase #7	$166.73	8.463%	$180.8404	$180.84	$180.85	$180.80
7 purchase totals =	$1,042.27		$1,117.5440	$1,117.53	$1,117.50	$1,117.60