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	$248.55	9.871%	$273.0844	$273.08	$273.10	$273.10
Purchase #2	$160.60	13.187%	$181.7783	$181.78	$181.80	$181.80
Purchase #3	$50.78	5.844%	$53.7476	$53.75	$53.75	$53.70
Purchase #4	$85.64	6.824%	$91.4841	$91.48	$91.50	$91.50
Purchase #5	$5.57	12.547%	$6.2689	$6.27	$6.25	$6.30
Purchase #6	$55.79	7.266%	$59.8437	$59.84	$59.85	$59.80
Purchase #7	$179.62	6.420%	$191.1516	$191.15	$191.15	$191.20
7 purchase totals =	$786.55		$857.3586	$857.35	$857.40	$857.40