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	$167.39	6.584%	$178.411	$178.41	$178.40	$178.40
Purchase #2	$100.54	11.728%	$112.3313	$112.33	$112.35	$112.30
Purchase #3	$133.34	7.546%	$143.4018	$143.40	$143.40	$143.40
Purchase #4	$250.67	8.738%	$272.5735	$272.57	$272.55	$272.60
Purchase #5	$6.56	4.380%	$6.8473	$6.85	$6.85	$6.80
Purchase #6	$141.40	13.761%	$160.8581	$160.86	$160.85	$160.90
Purchase #7	$134.89	8.191%	$145.9388	$145.94	$145.95	$145.90
7 purchase totals =	$934.79		$1,020.3618	$1,020.36	$1,020.35	$1,020.30