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	$71.96	13.232%	$81.4817	$81.48	$81.50	$81.50
Purchase #2	$62.85	13.153%	$71.1167	$71.12	$71.10	$71.10
Purchase #3	$41.27	9.120%	$45.0338	$45.03	$45.05	$45.00
Purchase #4	$85.60	12.138%	$95.9901	$95.99	$96.00	$96.00
Purchase #5	$221.59	13.666%	$251.8725	$251.87	$251.85	$251.90
Purchase #6	$222.95	12.304%	$250.3818	$250.38	$250.40	$250.40
Purchase #7	$232.46	4.302%	$242.4604	$242.46	$242.45	$242.50
7 purchase totals =	$938.68		$1,038.3370	$1,038.33	$1,038.35	$1,038.40