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	$45.25	11.765%	$50.5737	$50.57	$50.55	$50.60
Purchase #2	$187.92	13.617%	$213.5091	$213.51	$213.50	$213.50
Purchase #3	$128.46	7.121%	$137.6076	$137.61	$137.60	$137.60
Purchase #4	$238.33	10.368%	$263.0401	$263.04	$263.05	$263.00
Purchase #5	$138.46	10.394%	$152.8515	$152.85	$152.85	$152.90
Purchase #6	$23.34	9.214%	$25.4905	$25.49	$25.50	$25.50
Purchase #7	$191.37	7.780%	$206.2586	$206.26	$206.25	$206.30
7 purchase totals =	$953.13		$1,049.3311	$1,049.33	$1,049.30	$1,049.40