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	$80.55	5.259%	$84.7861	$84.79	$84.80	$84.80
Purchase #2	$228.42	9.489%	$250.0948	$250.09	$250.10	$250.10
Purchase #3	$99.91	9.719%	$109.6203	$109.62	$109.60	$109.60
Purchase #4	$221.40	4.454%	$231.2612	$231.26	$231.25	$231.30
Purchase #5	$165.86	11.590%	$185.0832	$185.08	$185.10	$185.10
Purchase #6	$206.77	5.385%	$217.9046	$217.90	$217.90	$217.90
Purchase #7	$249.46	12.479%	$280.5901	$280.59	$280.60	$280.60
7 purchase totals =	$1,252.37		$1,359.3403	$1,359.33	$1,359.35	$1,359.40