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	$72.81	7.755%	$78.4564	$78.46	$78.45	$78.50
Purchase #2	$176.33	4.848%	$184.8785	$184.88	$184.90	$184.90
Purchase #3	$156.60	7.195%	$167.8674	$167.87	$167.85	$167.90
Purchase #4	$130.61	8.231%	$141.3605	$141.36	$141.35	$141.40
Purchase #5	$215.92	7.742%	$232.6365	$232.64	$232.65	$232.60
Purchase #6	$74.96	10.386%	$82.7453	$82.75	$82.75	$82.70
Purchase #7	$249.85	7.558%	$268.7337	$268.73	$268.75	$268.70
7 purchase totals =	$1,077.08		$1,156.6783	$1,156.69	$1,156.70	$1,156.70