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	$27.67	13.498%	$31.4049	$31.40	$31.40	$31.40
Purchase #2	$173.57	7.262%	$186.1747	$186.17	$186.15	$186.20
Purchase #3	$52.40	13.238%	$59.3367	$59.34	$59.35	$59.30
Purchase #4	$93.98	10.391%	$103.7455	$103.75	$103.75	$103.70
Purchase #5	$88.61	4.427%	$92.5328	$92.53	$92.55	$92.50
Purchase #6	$167.61	8.212%	$181.3741	$181.37	$181.35	$181.40
Purchase #7	$150.91	9.505%	$165.254	$165.25	$165.25	$165.30
7 purchase totals =	$754.75		$819.8227	$819.81	$819.80	$819.80