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	$50.27	10.740%	$55.669	$55.67	$55.65	$55.70
Purchase #2	$72.75	8.165%	$78.69	$78.69	$78.70	$78.70
Purchase #3	$208.81	13.850%	$237.7302	$237.73	$237.75	$237.70
Purchase #4	$101.59	3.662%	$105.3102	$105.31	$105.30	$105.30
Purchase #5	$45.85	3.564%	$47.4841	$47.48	$47.50	$47.50
Purchase #6	$22.39	9.306%	$24.4736	$24.47	$24.45	$24.50
Purchase #7	$223.48	7.730%	$240.755	$240.76	$240.75	$240.80
7 purchase totals =	$725.14		$790.1121	$790.11	$790.10	$790.20