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	$12.54	8.437%	$13.598	$13.60	$13.60	$13.60
Purchase #2	$184.97	6.199%	$196.4363	$196.44	$196.45	$196.40
Purchase #3	$59.68	12.294%	$67.0171	$67.02	$67.00	$67.00
Purchase #4	$82.56	5.151%	$86.8127	$86.81	$86.80	$86.80
Purchase #5	$190.87	4.311%	$199.0984	$199.10	$199.10	$199.10
Purchase #6	$41.71	6.267%	$44.324	$44.32	$44.30	$44.30
Purchase #7	$209.33	6.454%	$222.8402	$222.84	$222.85	$222.80
7 purchase totals =	$781.66		$830.1267	$830.13	$830.10	$830.00