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	$85.73	4.280%	$89.3992	$89.40	$89.40	$89.40
Purchase #2	$237.46	7.402%	$255.0368	$255.04	$255.05	$255.00
Purchase #3	$47.97	9.631%	$52.59	$52.59	$52.60	$52.60
Purchase #4	$238.46	11.486%	$265.8495	$265.85	$265.85	$265.80
Purchase #5	$75.34	11.589%	$84.0712	$84.07	$84.05	$84.10
Purchase #6	$41.61	13.237%	$47.1179	$47.12	$47.10	$47.10
Purchase #7	$109.53	9.695%	$120.1489	$120.15	$120.15	$120.10
7 purchase totals =	$836.10		$914.2135	$914.22	$914.20	$914.10