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	$92.67	7.651%	$99.7602	$99.76	$99.75	$99.80
Purchase #2	$65.72	10.156%	$72.3945	$72.39	$72.40	$72.40
Purchase #3	$163.32	12.347%	$183.4851	$183.49	$183.50	$183.50
Purchase #4	$32.30	11.484%	$36.0093	$36.01	$36.00	$36.00
Purchase #5	$103.52	5.801%	$109.5252	$109.53	$109.55	$109.50
Purchase #6	$147.76	11.492%	$164.7406	$164.74	$164.75	$164.70
Purchase #7	$140.51	9.739%	$154.1943	$154.19	$154.20	$154.20
7 purchase totals =	$745.80		$820.1092	$820.11	$820.15	$820.10