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	$130.93	4.537%	$136.8703	$136.87	$136.85	$136.90
Purchase #2	$165.82	12.517%	$186.5757	$186.58	$186.60	$186.60
Purchase #3	$151.57	10.744%	$167.8547	$167.85	$167.85	$167.90
Purchase #4	$82.31	11.135%	$91.4752	$91.48	$91.50	$91.50
Purchase #5	$80.64	4.190%	$84.0188	$84.02	$84.00	$84.00
Purchase #6	$142.90	5.514%	$150.7795	$150.78	$150.80	$150.80
Purchase #7	$67.59	7.743%	$72.8235	$72.82	$72.80	$72.80
7 purchase totals =	$821.76		$890.3977	$890.40	$890.40	$890.50