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	$247.33	3.661%	$256.3848	$256.38	$256.40	$256.40
Purchase #2	$147.94	9.281%	$161.6703	$161.67	$161.65	$161.70
Purchase #3	$155.52	7.758%	$167.5852	$167.59	$167.60	$167.60
Purchase #4	$112.58	7.401%	$120.912	$120.91	$120.90	$120.90
Purchase #5	$68.68	5.447%	$72.421	$72.42	$72.40	$72.40
Purchase #6	$218.79	9.469%	$239.5072	$239.51	$239.50	$239.50
Purchase #7	$54.46	9.227%	$59.485	$59.49	$59.50	$59.50
7 purchase totals =	$1,005.30		$1,077.9655	$1,077.97	$1,077.95	$1,078.00