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	$239.56	10.820%	$265.4804	$265.48	$265.50	$265.50
Purchase #2	$40.26	7.253%	$43.1801	$43.18	$43.20	$43.20
Purchase #3	$138.56	8.450%	$150.2683	$150.27	$150.25	$150.30
Purchase #4	$179.40	11.686%	$200.3647	$200.36	$200.35	$200.40
Purchase #5	$97.77	9.625%	$107.1804	$107.18	$107.20	$107.20
Purchase #6	$169.86	11.195%	$188.8758	$188.88	$188.90	$188.90
Purchase #7	$95.59	3.678%	$99.1058	$99.11	$99.10	$99.10
7 purchase totals =	$961.00		$1,054.4555	$1,054.46	$1,054.50	$1,054.60