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	$152.49	6.489%	$162.3851	$162.39	$162.40	$162.40
Purchase #2	$49.61	3.186%	$51.1906	$51.19	$51.20	$51.20
Purchase #3	$215.91	3.648%	$223.7864	$223.79	$223.80	$223.80
Purchase #4	$249.73	7.825%	$269.2714	$269.27	$269.25	$269.30
Purchase #5	$227.26	5.756%	$240.3411	$240.34	$240.35	$240.30
Purchase #6	$141.96	12.330%	$159.4637	$159.46	$159.45	$159.50
Purchase #7	$63.61	13.458%	$72.1706	$72.17	$72.15	$72.20
7 purchase totals =	$1,100.57		$1,178.6089	$1,178.61	$1,178.60	$1,178.70