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	$110.69	5.206%	$116.4525	$116.45	$116.45	$116.50
Purchase #2	$231.40	13.792%	$263.3147	$263.31	$263.30	$263.30
Purchase #3	$99.71	13.658%	$113.3284	$113.33	$113.35	$113.30
Purchase #4	$96.59	4.392%	$100.8322	$100.83	$100.85	$100.80
Purchase #5	$47.84	7.458%	$51.4079	$51.41	$51.40	$51.40
Purchase #6	$232.55	9.132%	$253.7865	$253.79	$253.80	$253.80
Purchase #7	$21.94	12.588%	$24.7018	$24.70	$24.70	$24.70
7 purchase totals =	$840.72		$923.8240	$923.82	$923.85	$923.80