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	$201.94	12.541%	$227.2653	$227.27	$227.25	$227.30
Purchase #2	$52.26	11.736%	$58.3932	$58.39	$58.40	$58.40
Purchase #3	$246.67	9.383%	$269.815	$269.82	$269.80	$269.80
Purchase #4	$207.78	11.600%	$231.8825	$231.88	$231.90	$231.90
Purchase #5	$180.60	5.191%	$189.9749	$189.97	$189.95	$190.00
Purchase #6	$80.36	11.793%	$89.8369	$89.84	$89.85	$89.80
Purchase #7	$129.72	9.224%	$141.6854	$141.69	$141.70	$141.70
7 purchase totals =	$1,099.33		$1,208.8532	$1,208.86	$1,208.85	$1,208.90