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	$155.95	7.648%	$167.8771	$167.88	$167.90	$167.90
Purchase #2	$94.34	4.170%	$98.274	$98.27	$98.25	$98.30
Purchase #3	$164.70	11.863%	$184.2384	$184.24	$184.25	$184.20
Purchase #4	$174.76	12.212%	$196.1017	$196.10	$196.10	$196.10
Purchase #5	$209.29	4.587%	$218.8901	$218.89	$218.90	$218.90
Purchase #6	$221.42	9.380%	$242.1892	$242.19	$242.20	$242.20
Purchase #7	$31.98	3.455%	$33.0849	$33.08	$33.10	$33.10
7 purchase totals =	$1,052.44		$1,140.6554	$1,140.65	$1,140.70	$1,140.70