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	$101.60	10.630%	$112.4001	$112.40	$112.40	$112.40
Purchase #2	$135.89	7.309%	$145.8222	$145.82	$145.80	$145.80
Purchase #3	$239.32	4.636%	$250.4149	$250.41	$250.40	$250.40
Purchase #4	$93.72	13.728%	$106.5859	$106.59	$106.60	$106.60
Purchase #5	$84.73	3.401%	$87.6117	$87.61	$87.60	$87.60
Purchase #6	$184.59	10.673%	$204.2913	$204.29	$204.30	$204.30
Purchase #7	$219.47	10.874%	$243.3352	$243.34	$243.35	$243.30
7 purchase totals =	$1,059.32		$1,150.4613	$1,150.46	$1,150.45	$1,150.40