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	$128.94	8.298%	$139.6394	$139.64	$139.65	$139.60
Purchase #2	$82.62	11.109%	$91.7983	$91.80	$91.80	$91.80
Purchase #3	$221.65	9.685%	$243.1168	$243.12	$243.10	$243.10
Purchase #4	$162.74	4.294%	$169.7281	$169.73	$169.75	$169.70
Purchase #5	$107.77	11.245%	$119.8887	$119.89	$119.90	$119.90
Purchase #6	$27.87	11.418%	$31.0522	$31.05	$31.05	$31.10
Purchase #7	$248.64	6.830%	$265.6221	$265.62	$265.60	$265.60
7 purchase totals =	$980.23		$1,060.8456	$1,060.85	$1,060.85	$1,060.80