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	$72.70	13.232%	$82.3197	$82.32	$82.30	$82.30
Purchase #2	$117.82	9.162%	$128.6147	$128.61	$128.60	$128.60
Purchase #3	$120.95	13.179%	$136.89	$136.89	$136.90	$136.90
Purchase #4	$247.64	9.184%	$270.3833	$270.38	$270.40	$270.40
Purchase #5	$163.78	11.256%	$182.2151	$182.22	$182.20	$182.20
Purchase #6	$86.77	7.648%	$93.4062	$93.41	$93.40	$93.40
Purchase #7	$85.25	5.525%	$89.9601	$89.96	$89.95	$90.00
7 purchase totals =	$894.91		$983.7891	$983.79	$983.75	$983.80