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	$174.91	6.286%	$185.9048	$185.90	$185.90	$185.90
Purchase #2	$159.47	4.289%	$166.3097	$166.31	$166.30	$166.30
Purchase #3	$81.76	11.710%	$91.3341	$91.33	$91.35	$91.30
Purchase #4	$245.25	10.500%	$271.0013	$271.00	$271.00	$271.00
Purchase #5	$226.82	10.430%	$250.4773	$250.48	$250.50	$250.50
Purchase #6	$161.73	10.159%	$178.1602	$178.16	$178.15	$178.20
Purchase #7	$106.43	9.548%	$116.5919	$116.59	$116.60	$116.60
7 purchase totals =	$1,156.37		$1,259.7793	$1,259.77	$1,259.80	$1,259.80