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	$51.54	12.401%	$57.9315	$57.93	$57.95	$57.90
Purchase #2	$203.82	12.310%	$228.9102	$228.91	$228.90	$228.90
Purchase #3	$54.53	12.780%	$61.4989	$61.50	$61.50	$61.50
Purchase #4	$209.72	8.522%	$227.5923	$227.59	$227.60	$227.60
Purchase #5	$43.87	13.698%	$49.8793	$49.88	$49.90	$49.90
Purchase #6	$37.75	12.742%	$42.5601	$42.56	$42.55	$42.60
Purchase #7	$202.91	5.334%	$213.7332	$213.73	$213.75	$213.70
7 purchase totals =	$804.14		$882.1055	$882.10	$882.15	$882.10