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	$229.83	13.543%	$260.9559	$260.96	$260.95	$261.00
Purchase #2	$33.89	6.540%	$36.1064	$36.11	$36.10	$36.10
Purchase #3	$202.83	3.396%	$209.7181	$209.72	$209.70	$209.70
Purchase #4	$25.38	10.706%	$28.0972	$28.10	$28.10	$28.10
Purchase #5	$50.90	3.780%	$52.824	$52.82	$52.80	$52.80
Purchase #6	$242.27	13.107%	$274.0243	$274.02	$274.00	$274.00
Purchase #7	$63.86	4.651%	$66.8301	$66.83	$66.85	$66.80
7 purchase totals =	$848.96		$928.5560	$928.56	$928.50	$928.50