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	$135.28	3.334%	$139.7902	$139.79	$139.80	$139.80
Purchase #2	$85.97	12.208%	$96.4652	$96.47	$96.45	$96.50
Purchase #3	$53.39	11.763%	$59.6703	$59.67	$59.65	$59.70
Purchase #4	$225.90	6.567%	$240.7349	$240.73	$240.75	$240.70
Purchase #5	$63.27	7.413%	$67.9602	$67.96	$67.95	$68.00
Purchase #6	$102.90	12.360%	$115.6184	$115.62	$115.60	$115.60
Purchase #7	$109.51	13.123%	$123.881	$123.88	$123.90	$123.90
7 purchase totals =	$776.22		$844.1202	$844.12	$844.10	$844.20