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	$35.75	12.802%	$40.3267	$40.33	$40.35	$40.30
Purchase #2	$77.85	10.216%	$85.8032	$85.80	$85.80	$85.80
Purchase #3	$245.28	9.469%	$268.5056	$268.51	$268.50	$268.50
Purchase #4	$119.26	9.391%	$130.4597	$130.46	$130.45	$130.50
Purchase #5	$206.49	10.469%	$228.1074	$228.11	$228.10	$228.10
Purchase #6	$110.32	5.651%	$116.5542	$116.55	$116.55	$116.60
Purchase #7	$132.87	6.646%	$141.7005	$141.70	$141.70	$141.70
7 purchase totals =	$927.82		$1,011.4573	$1,011.46	$1,011.45	$1,011.50