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	$212.42	6.806%	$226.8773	$226.88	$226.90	$226.90
Purchase #2	$191.53	4.314%	$199.7926	$199.79	$199.80	$199.80
Purchase #3	$39.91	4.869%	$41.8532	$41.85	$41.85	$41.90
Purchase #4	$53.79	10.511%	$59.4439	$59.44	$59.45	$59.40
Purchase #5	$189.90	5.690%	$200.7053	$200.71	$200.70	$200.70
Purchase #6	$25.98	5.348%	$27.3694	$27.37	$27.35	$27.40
Purchase #7	$39.48	5.193%	$41.5302	$41.53	$41.55	$41.50
7 purchase totals =	$753.01		$797.5719	$797.57	$797.60	$797.60