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	$35.75	5.854%	$37.8428	$37.84	$37.85	$37.80
Purchase #2	$33.86	10.395%	$37.3797	$37.38	$37.40	$37.40
Purchase #3	$112.42	7.129%	$120.4344	$120.43	$120.45	$120.40
Purchase #4	$93.35	4.400%	$97.4574	$97.46	$97.45	$97.50
Purchase #5	$188.28	6.684%	$200.8646	$200.86	$200.85	$200.90
Purchase #6	$227.32	10.331%	$250.8044	$250.80	$250.80	$250.80
Purchase #7	$226.54	6.131%	$240.4292	$240.43	$240.45	$240.40
7 purchase totals =	$917.52		$985.2125	$985.20	$985.25	$985.20