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	$5.53	9.510%	$6.0559	$6.06	$6.05	$6.10
Purchase #2	$101.92	7.693%	$109.7607	$109.76	$109.75	$109.80
Purchase #3	$45.39	10.768%	$50.2776	$50.28	$50.30	$50.30
Purchase #4	$136.54	3.744%	$141.6521	$141.65	$141.65	$141.70
Purchase #5	$130.46	8.771%	$141.9026	$141.90	$141.90	$141.90
Purchase #6	$42.60	12.466%	$47.9105	$47.91	$47.90	$47.90
Purchase #7	$53.73	10.316%	$59.2728	$59.27	$59.25	$59.30
7 purchase totals =	$516.17		$556.8322	$556.83	$556.80	$557.00