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	$234.55	13.639%	$266.5403	$266.54	$266.55	$266.50
Purchase #2	$151.33	3.400%	$156.4752	$156.48	$156.50	$156.50
Purchase #3	$85.54	4.789%	$89.6365	$89.64	$89.65	$89.60
Purchase #4	$136.63	5.279%	$143.8427	$143.84	$143.85	$143.80
Purchase #5	$78.33	10.797%	$86.7873	$86.79	$86.80	$86.80
Purchase #6	$247.50	7.110%	$265.0973	$265.10	$265.10	$265.10
Purchase #7	$39.62	5.869%	$41.9453	$41.95	$41.95	$41.90
7 purchase totals =	$973.50		$1,050.3246	$1,050.34	$1,050.40	$1,050.20