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	$16.48	13.839%	$18.7607	$18.76	$18.75	$18.80
Purchase #2	$176.76	3.185%	$182.3898	$182.39	$182.40	$182.40
Purchase #3	$59.63	13.788%	$67.8518	$67.85	$67.85	$67.90
Purchase #4	$57.86	12.548%	$65.1203	$65.12	$65.10	$65.10
Purchase #5	$161.75	3.567%	$167.5196	$167.52	$167.50	$167.50
Purchase #6	$106.33	9.216%	$116.1294	$116.13	$116.15	$116.10
Purchase #7	$117.43	5.164%	$123.4941	$123.49	$123.50	$123.50
7 purchase totals =	$696.24		$741.2657	$741.26	$741.25	$741.30