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	$165.96	9.262%	$181.3312	$181.33	$181.35	$181.30
Purchase #2	$35.33	12.778%	$39.8445	$39.84	$39.85	$39.80
Purchase #3	$60.44	10.601%	$66.8472	$66.85	$66.85	$66.80
Purchase #4	$27.96	7.486%	$30.0531	$30.05	$30.05	$30.10
Purchase #5	$182.71	7.444%	$196.3109	$196.31	$196.30	$196.30
Purchase #6	$54.78	10.603%	$60.5883	$60.59	$60.60	$60.60
Purchase #7	$236.46	3.789%	$245.4195	$245.42	$245.40	$245.40
7 purchase totals =	$763.64		$820.3947	$820.39	$820.40	$820.30