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	$181.83	9.828%	$199.7003	$199.70	$199.70	$199.70
Purchase #2	$83.67	7.454%	$89.9068	$89.91	$89.90	$89.90
Purchase #3	$73.59	12.168%	$82.5444	$82.54	$82.55	$82.50
Purchase #4	$150.74	11.204%	$167.6289	$167.63	$167.65	$167.60
Purchase #5	$25.33	10.116%	$27.8924	$27.89	$27.90	$27.90
Purchase #6	$70.47	13.498%	$79.982	$79.98	$80.00	$80.00
Purchase #7	$118.32	3.569%	$122.5428	$122.54	$122.55	$122.50
7 purchase totals =	$703.95		$770.1976	$770.19	$770.25	$770.10