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	$250.61	9.432%	$274.2475	$274.25	$274.25	$274.20
Purchase #2	$201.30	4.140%	$209.6338	$209.63	$209.65	$209.60
Purchase #3	$37.35	13.866%	$42.529	$42.53	$42.55	$42.50
Purchase #4	$198.81	4.483%	$207.7227	$207.72	$207.70	$207.70
Purchase #5	$176.39	11.642%	$196.9253	$196.93	$196.95	$196.90
Purchase #6	$106.40	4.155%	$110.8209	$110.82	$110.80	$110.80
Purchase #7	$134.63	6.587%	$143.4981	$143.50	$143.50	$143.50
7 purchase totals =	$1,105.49		$1,185.3773	$1,185.38	$1,185.40	$1,185.20