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	$157.35	11.729%	$175.8056	$175.81	$175.80	$175.80
Purchase #2	$200.74	13.352%	$227.5428	$227.54	$227.55	$227.50
Purchase #3	$38.82	9.535%	$42.5215	$42.52	$42.50	$42.50
Purchase #4	$96.94	4.535%	$101.3362	$101.34	$101.35	$101.30
Purchase #5	$144.90	10.615%	$160.2811	$160.28	$160.30	$160.30
Purchase #6	$78.57	9.196%	$85.7953	$85.80	$85.80	$85.80
Purchase #7	$97.71	12.330%	$109.7576	$109.76	$109.75	$109.80
7 purchase totals =	$815.03		$903.0401	$903.05	$903.05	$903.00