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	$48.44	12.223%	$54.3608	$54.36	$54.35	$54.40
Purchase #2	$73.62	9.776%	$80.8171	$80.82	$80.80	$80.80
Purchase #3	$47.40	10.199%	$52.2343	$52.23	$52.25	$52.20
Purchase #4	$45.30	11.564%	$50.5385	$50.54	$50.55	$50.50
Purchase #5	$162.63	13.284%	$184.2338	$184.23	$184.25	$184.20
Purchase #6	$203.35	8.597%	$220.832	$220.83	$220.85	$220.80
Purchase #7	$82.64	8.469%	$89.6388	$89.64	$89.65	$89.60
7 purchase totals =	$663.38		$732.6553	$732.65	$732.70	$732.50