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	$48.60	6.566%	$51.7911	$51.79	$51.80	$51.80
Purchase #2	$119.82	9.567%	$131.2832	$131.28	$131.30	$131.30
Purchase #3	$199.61	6.440%	$212.4649	$212.46	$212.45	$212.50
Purchase #4	$61.38	10.157%	$67.6144	$67.61	$67.60	$67.60
Purchase #5	$77.42	5.645%	$81.7904	$81.79	$81.80	$81.80
Purchase #6	$156.27	9.622%	$171.3063	$171.31	$171.30	$171.30
Purchase #7	$211.39	5.417%	$222.841	$222.84	$222.85	$222.80
7 purchase totals =	$874.49		$939.0913	$939.08	$939.10	$939.10