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	$180.54	4.198%	$188.1191	$188.12	$188.10	$188.10
Purchase #2	$220.72	12.570%	$248.4645	$248.46	$248.45	$248.50
Purchase #3	$223.45	12.264%	$250.8539	$250.85	$250.85	$250.90
Purchase #4	$248.84	12.304%	$279.4573	$279.46	$279.45	$279.50
Purchase #5	$19.63	7.661%	$21.1339	$21.13	$21.15	$21.10
Purchase #6	$44.74	13.535%	$50.7956	$50.80	$50.80	$50.80
Purchase #7	$68.53	3.642%	$71.0259	$71.03	$71.05	$71.00
7 purchase totals =	$1,006.45		$1,109.8502	$1,109.85	$1,109.85	$1,109.90