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	$102.75	6.680%	$109.6137	$109.61	$109.60	$109.60
Purchase #2	$69.94	3.259%	$72.2193	$72.22	$72.20	$72.20
Purchase #3	$135.47	12.841%	$152.8657	$152.87	$152.85	$152.90
Purchase #4	$59.34	3.743%	$61.5611	$61.56	$61.55	$61.60
Purchase #5	$14.89	5.785%	$15.7514	$15.75	$15.75	$15.80
Purchase #6	$239.91	12.802%	$270.6233	$270.62	$270.60	$270.60
Purchase #7	$166.47	5.379%	$175.4244	$175.42	$175.40	$175.40
7 purchase totals =	$788.77		$858.0589	$858.05	$857.95	$858.10