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	$154.58	13.135%	$174.8841	$174.88	$174.90	$174.90
Purchase #2	$102.87	6.291%	$109.3416	$109.34	$109.35	$109.30
Purchase #3	$157.76	12.601%	$177.6393	$177.64	$177.65	$177.60
Purchase #4	$186.62	11.783%	$208.6094	$208.61	$208.60	$208.60
Purchase #5	$120.43	13.570%	$136.7724	$136.77	$136.75	$136.80
Purchase #6	$76.27	9.834%	$83.7704	$83.77	$83.75	$83.80
Purchase #7	$200.54	4.304%	$209.1712	$209.17	$209.15	$209.20
7 purchase totals =	$999.07		$1,100.1884	$1,100.18	$1,100.15	$1,100.20