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	$12.35	10.119%	$13.5997	$13.60	$13.60	$13.60
Purchase #2	$158.41	6.402%	$168.5514	$168.55	$168.55	$168.60
Purchase #3	$250.54	9.257%	$273.7325	$273.73	$273.75	$273.70
Purchase #4	$167.56	6.270%	$178.066	$178.07	$178.05	$178.10
Purchase #5	$166.75	10.727%	$184.6373	$184.64	$184.65	$184.60
Purchase #6	$130.27	9.814%	$143.0547	$143.05	$143.05	$143.10
Purchase #7	$106.42	7.830%	$114.7527	$114.75	$114.75	$114.80
7 purchase totals =	$992.30		$1,076.3943	$1,076.39	$1,076.40	$1,076.50