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	$150.71	9.666%	$165.2776	$165.28	$165.30	$165.30
Purchase #2	$36.88	5.419%	$38.8785	$38.88	$38.90	$38.90
Purchase #3	$5.33	3.375%	$5.5099	$5.51	$5.50	$5.50
Purchase #4	$187.39	12.337%	$210.5083	$210.51	$210.50	$210.50
Purchase #5	$23.79	6.209%	$25.2671	$25.27	$25.25	$25.30
Purchase #6	$29.85	12.189%	$33.4884	$33.49	$33.50	$33.50
Purchase #7	$34.88	6.588%	$37.1779	$37.18	$37.20	$37.20
7 purchase totals =	$468.83		$516.1077	$516.12	$516.15	$516.20