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	$132.63	4.744%	$138.922	$138.92	$138.90	$138.90
Purchase #2	$154.74	7.640%	$166.5621	$166.56	$166.55	$166.60
Purchase #3	$177.80	4.387%	$185.6001	$185.60	$185.60	$185.60
Purchase #4	$185.30	6.185%	$196.7608	$196.76	$196.75	$196.80
Purchase #5	$157.74	5.696%	$166.7249	$166.72	$166.70	$166.70
Purchase #6	$123.34	9.393%	$134.9253	$134.93	$134.95	$134.90
Purchase #7	$216.46	12.606%	$243.7469	$243.75	$243.75	$243.70
7 purchase totals =	$1,148.01		$1,233.2421	$1,233.24	$1,233.20	$1,233.20