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	$236.46	11.830%	$264.4332	$264.43	$264.45	$264.40
Purchase #2	$195.67	6.855%	$209.0832	$209.08	$209.10	$209.10
Purchase #3	$30.65	9.857%	$33.6712	$33.67	$33.65	$33.70
Purchase #4	$222.28	10.409%	$245.4171	$245.42	$245.40	$245.40
Purchase #5	$243.29	10.363%	$268.5021	$268.50	$268.50	$268.50
Purchase #6	$95.67	4.806%	$100.2679	$100.27	$100.25	$100.30
Purchase #7	$164.96	13.288%	$186.8799	$186.88	$186.90	$186.90
7 purchase totals =	$1,188.98		$1,308.2546	$1,308.25	$1,308.25	$1,308.30