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	$101.85	9.702%	$111.7315	$111.73	$111.75	$111.70
Purchase #2	$52.96	12.311%	$59.4799	$59.48	$59.50	$59.50
Purchase #3	$74.44	5.867%	$78.8074	$78.81	$78.80	$78.80
Purchase #4	$222.95	4.862%	$233.7898	$233.79	$233.80	$233.80
Purchase #5	$14.67	8.393%	$15.9013	$15.90	$15.90	$15.90
Purchase #6	$82.34	4.842%	$86.3269	$86.33	$86.35	$86.30
Purchase #7	$230.44	6.503%	$245.4255	$245.43	$245.45	$245.40
7 purchase totals =	$779.65		$831.4623	$831.47	$831.55	$831.40