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	$84.44	6.384%	$89.8306	$89.83	$89.85	$89.80
Purchase #2	$99.44	10.302%	$109.6843	$109.68	$109.70	$109.70
Purchase #3	$116.56	10.580%	$128.892	$128.89	$128.90	$128.90
Purchase #4	$131.67	6.164%	$139.7861	$139.79	$139.80	$139.80
Purchase #5	$62.42	11.646%	$69.6894	$69.69	$69.70	$69.70
Purchase #6	$130.53	11.611%	$145.6858	$145.69	$145.70	$145.70
Purchase #7	$148.53	12.760%	$167.4824	$167.48	$167.50	$167.50
7 purchase totals =	$773.59		$851.0506	$851.05	$851.15	$851.10