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	$175.86	6.259%	$186.8671	$186.87	$186.85	$186.90
Purchase #2	$229.98	4.764%	$240.9362	$240.94	$240.95	$240.90
Purchase #3	$161.35	4.473%	$168.5672	$168.57	$168.55	$168.60
Purchase #4	$50.60	12.363%	$56.8557	$56.86	$56.85	$56.90
Purchase #5	$19.71	9.474%	$21.5773	$21.58	$21.60	$21.60
Purchase #6	$41.46	3.133%	$42.7589	$42.76	$42.75	$42.80
Purchase #7	$90.54	8.289%	$98.0449	$98.04	$98.05	$98.00
7 purchase totals =	$769.50		$815.6073	$815.62	$815.60	$815.70