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	$42.55	10.112%	$46.8527	$46.85	$46.85	$46.90
Purchase #2	$155.89	6.506%	$166.0322	$166.03	$166.05	$166.00
Purchase #3	$188.33	6.494%	$200.5602	$200.56	$200.55	$200.60
Purchase #4	$25.57	6.833%	$27.3172	$27.32	$27.30	$27.30
Purchase #5	$166.80	8.741%	$181.38	$181.38	$181.40	$181.40
Purchase #6	$247.53	8.225%	$267.8893	$267.89	$267.90	$267.90
Purchase #7	$21.40	11.298%	$23.8178	$23.82	$23.80	$23.80
7 purchase totals =	$848.07		$913.8494	$913.85	$913.85	$913.90