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	$55.88	6.269%	$59.3831	$59.38	$59.40	$59.40
Purchase #2	$153.88	11.192%	$171.1022	$171.10	$171.10	$171.10
Purchase #3	$89.98	10.654%	$99.5665	$99.57	$99.55	$99.60
Purchase #4	$121.52	6.706%	$129.6691	$129.67	$129.65	$129.70
Purchase #5	$80.88	5.666%	$85.4627	$85.46	$85.45	$85.50
Purchase #6	$76.66	11.751%	$85.6683	$85.67	$85.65	$85.70
Purchase #7	$188.84	5.442%	$199.1167	$199.12	$199.10	$199.10
7 purchase totals =	$767.64		$829.9686	$829.97	$829.90	$830.10