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	$92.90	11.357%	$103.4507	$103.45	$103.45	$103.50
Purchase #2	$153.44	5.630%	$162.0787	$162.08	$162.10	$162.10
Purchase #3	$130.71	12.376%	$146.8867	$146.89	$146.90	$146.90
Purchase #4	$133.76	4.179%	$139.3498	$139.35	$139.35	$139.30
Purchase #5	$27.96	8.707%	$30.3945	$30.39	$30.40	$30.40
Purchase #6	$17.75	3.138%	$18.307	$18.31	$18.30	$18.30
Purchase #7	$213.89	3.585%	$221.558	$221.56	$221.55	$221.60
7 purchase totals =	$770.41		$822.0254	$822.03	$822.05	$822.10