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	$81.82	13.414%	$92.7953	$92.80	$92.80	$92.80
Purchase #2	$113.55	8.528%	$123.2335	$123.23	$123.25	$123.20
Purchase #3	$128.26	11.679%	$143.2395	$143.24	$143.25	$143.20
Purchase #4	$177.43	3.291%	$183.2692	$183.27	$183.25	$183.30
Purchase #5	$53.86	11.159%	$59.8702	$59.87	$59.85	$59.90
Purchase #6	$101.97	7.684%	$109.8054	$109.81	$109.80	$109.80
Purchase #7	$135.41	3.252%	$139.8135	$139.81	$139.80	$139.80
7 purchase totals =	$792.30		$852.0266	$852.03	$852.00	$852.00