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	$221.78	12.712%	$249.9727	$249.97	$249.95	$250.00
Purchase #2	$217.61	10.634%	$240.7506	$240.75	$240.75	$240.80
Purchase #3	$106.35	6.165%	$112.9065	$112.91	$112.90	$112.90
Purchase #4	$234.26	12.219%	$262.8842	$262.88	$262.90	$262.90
Purchase #5	$85.90	4.356%	$89.6418	$89.64	$89.65	$89.60
Purchase #6	$72.63	6.835%	$77.5943	$77.59	$77.60	$77.60
Purchase #7	$187.48	4.849%	$196.5709	$196.57	$196.55	$196.60
7 purchase totals =	$1,126.01		$1,230.3210	$1,230.31	$1,230.30	$1,230.40