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	$36.51	11.651%	$40.7638	$40.76	$40.75	$40.80
Purchase #2	$242.34	11.292%	$269.705	$269.71	$269.70	$269.70
Purchase #3	$112.73	6.801%	$120.3968	$120.40	$120.40	$120.40
Purchase #4	$68.31	9.567%	$74.8452	$74.85	$74.85	$74.80
Purchase #5	$89.90	7.808%	$96.9194	$96.92	$96.90	$96.90
Purchase #6	$174.98	6.691%	$186.6879	$186.69	$186.70	$186.70
Purchase #7	$186.57	5.307%	$196.4713	$196.47	$196.45	$196.50
7 purchase totals =	$911.34		$985.7894	$985.80	$985.75	$985.80