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	$85.46	9.520%	$93.5958	$93.60	$93.60	$93.60
Purchase #2	$223.93	11.860%	$250.4881	$250.49	$250.50	$250.50
Purchase #3	$125.65	13.729%	$142.9005	$142.90	$142.90	$142.90
Purchase #4	$185.68	9.590%	$203.4867	$203.49	$203.50	$203.50
Purchase #5	$223.30	7.342%	$239.6947	$239.69	$239.70	$239.70
Purchase #6	$67.31	7.433%	$72.3132	$72.31	$72.30	$72.30
Purchase #7	$131.95	8.668%	$143.3874	$143.39	$143.40	$143.40
7 purchase totals =	$1,043.28		$1,145.8664	$1,145.87	$1,145.90	$1,145.90