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	$105.70	11.525%	$117.8819	$117.88	$117.90	$117.90
Purchase #2	$161.53	6.666%	$172.2976	$172.30	$172.30	$172.30
Purchase #3	$144.30	8.298%	$156.274	$156.27	$156.25	$156.30
Purchase #4	$92.85	3.669%	$96.2567	$96.26	$96.25	$96.30
Purchase #5	$166.55	4.681%	$174.3462	$174.35	$174.35	$174.30
Purchase #6	$69.96	12.746%	$78.8771	$78.88	$78.90	$78.90
Purchase #7	$30.33	3.130%	$31.2793	$31.28	$31.30	$31.30
7 purchase totals =	$771.22		$827.2128	$827.22	$827.25	$827.30