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	$184.92	13.810%	$210.4575	$210.46	$210.45	$210.50
Purchase #2	$96.69	9.480%	$105.8562	$105.86	$105.85	$105.90
Purchase #3	$99.63	9.799%	$109.3927	$109.39	$109.40	$109.40
Purchase #4	$123.96	13.451%	$140.6339	$140.63	$140.65	$140.60
Purchase #5	$102.64	4.572%	$107.3327	$107.33	$107.35	$107.30
Purchase #6	$48.59	7.165%	$52.0715	$52.07	$52.05	$52.10
Purchase #7	$191.89	11.218%	$213.4162	$213.42	$213.40	$213.40
7 purchase totals =	$848.32		$939.1607	$939.16	$939.15	$939.20