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	$37.60	12.623%	$42.3462	$42.35	$42.35	$42.30
Purchase #2	$153.50	11.813%	$171.633	$171.63	$171.65	$171.60
Purchase #3	$202.44	11.525%	$225.7712	$225.77	$225.75	$225.80
Purchase #4	$236.65	12.351%	$265.8786	$265.88	$265.90	$265.90
Purchase #5	$69.81	12.285%	$78.3862	$78.39	$78.40	$78.40
Purchase #6	$157.79	6.485%	$168.0227	$168.02	$168.00	$168.00
Purchase #7	$114.71	8.430%	$124.3801	$124.38	$124.40	$124.40
7 purchase totals =	$972.50		$1,076.4180	$1,076.42	$1,076.45	$1,076.40