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	$175.51	6.357%	$186.6672	$186.67	$186.65	$186.70
Purchase #2	$143.36	13.359%	$162.5115	$162.51	$162.50	$162.50
Purchase #3	$29.84	11.870%	$33.382	$33.38	$33.40	$33.40
Purchase #4	$151.68	5.451%	$159.9481	$159.95	$159.95	$159.90
Purchase #5	$81.85	13.346%	$92.7737	$92.77	$92.75	$92.80
Purchase #6	$30.63	10.681%	$33.9016	$33.90	$33.90	$33.90
Purchase #7	$115.75	13.610%	$131.5036	$131.50	$131.50	$131.50
7 purchase totals =	$728.62		$800.6877	$800.68	$800.65	$800.70