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	$45.33	13.517%	$51.4573	$51.46	$51.45	$51.50
Purchase #2	$100.83	11.319%	$112.2429	$112.24	$112.25	$112.20
Purchase #3	$128.86	8.585%	$139.9226	$139.92	$139.90	$139.90
Purchase #4	$218.93	8.398%	$237.3157	$237.32	$237.30	$237.30
Purchase #5	$184.39	13.635%	$209.5316	$209.53	$209.55	$209.50
Purchase #6	$39.81	4.712%	$41.6858	$41.69	$41.70	$41.70
Purchase #7	$130.39	6.872%	$139.3504	$139.35	$139.35	$139.40
7 purchase totals =	$848.54		$931.5063	$931.51	$931.50	$931.50